Should I stop the "fight"?

They are probably trying to establish there dominance, and sometimes letting it go can solve the problem. 
 
BUT....since there is no way for me to actually see what's going on I can not tell you to let them go at it.  You can only let them go as far as you are comfortable with.
 
This is going to continue to get worse if you don't take some action one way or another. I would get a little help right away.  The more severe it gets the harder it will be to stop.

Mic knows FAR more than I do but, if I were in your situation, I would probably let them sort it out on their own.  Up to a point anyway.  That point, for me, would be if they draw blood.

The biggest thing I can tell you Sandra (like Mic without seeing whats going on) is this. As a general rule, when females fight - they mean it.

Thank you so much for responding so promptly. 
 
Mic, by help do you mean consulting a behaviorist?  The scuffles aren't a daily occurance so I'm not sure that if I had one come over there would be anything to see... I certainly don't want these little skirmishes to get any worse (this morning's little arguement shook me up a little).  Do you think I should look into a behaviorist?  Are they outrageously expensive?

I think it will get worse...so I would seriously consider getting some help from a behaviorist.  I wouldn't wait until it gets bad. 
 
A good behaviorist won't actually need to see the scuffle.  They should be able to evaluate YOU and the dogs and set up some protocols to help you resolve the problem. 
 
Prices are going to vary depending on the level of expertise you hire and where they are located.  It can be expensive. I'll pm you with our prices.

Mic, how does one go about finding a good behaviorist (I sure wish you were in upstate NY and not Ohio!)?  Should I call my vet for a referral?  I certainly don't want this to get any worse, and I want to keep Zoey if at all possible. Although, it is very comforting to know that since I got her from a rescue, if I absolutely can not get this to work out, that they will take her back and rehome her. But I really, really don't want it to come to that- we already love her!

Calling your vet is a good option.  I did a consult in Buffalo a few weeks ago, but didn't have an opportunity to speak with any local professionals. Anne may have some ideas for you.  I sent you an email in regard to prices.

Thank you so much.  I live in central New York, Syracuse area.  Do you know anyone there?

Sandra - I'm really sorry you're experiencing this.  I truly know how frightening it can be.  The fights between my two dogs, Buffy & Sassy, are actually what first brought me to idog about 4 years ago.  Your description sounds very much like what we've seen, so I'll only tell you how it's been for us.  When we rescued Sassy, she was about 2 (a lovable lab).  Buffy was 6 and also a sweetheart who'd gotten along with our male lab until he passed away.  Buffy & Sassy seemed to hit it off just fine.  Then one day, sort of maneuvering to get pets from my husband, they broke into a fight.  There were more after that, separated by weeks, sometimes by a month or two and provoked by anything from a toy, treat, loud noise or sometimes by nothing we could see.  We took them both to a behaviorist and based on her observations, we decided to not rehome Sassy, but it has been far from easy.  The behaviorist said that a) they seem to like each other; b) they are females and sometimes they're just not going to get along; c) it was imperative that we keep fights from happening as much as possible.  She said that each fight, especially if it draws blood, breaks down the barriers that will prevent it from happening again.  So, we keep them separated when we're not there and never allow them to eat near each other, have treats together and even are careful to play with them together.  In the last year they've only had 3 fights.  The last one was the most puzzling to me and although it was last Sept., it has stuck with me more than any other.  I made a decision at that time that I would not allow them to be together when my husband isn't home.  I always knew I'd have trouble breaking up a fight between them (Buffy weighs 65 lbs and Sassy weighs 75 lbs), but the last one made me realize that I can't even anticipate the triggers very well.  It's just too unnerving for me to be alone with them worrying about what might happen.
 
So - I'm probably not making you feel too good about this, but I just wanted to share my experience.  We love these dogs with all our heart, but I'm not sure that if I had it to do over again, I wouldn't have rehomed Sassy.  Like you, we fell in love with her very quickly (especially my husband) and couldn't bear to give her away.  I would definitely consult with a behaviorist though and I think the cost was about $90 but worth every penny.
 
Good luck with however this works out for you!

If she has to go back to the rescue, I'd rather it be sooner than later but I cry when I consider it at all.  But I also want my dogs to be happy (and safe) and need to consider my resident dogs first as they have been living peacefully here for over a year.

I would take Mic's advice, plus --- until you have your situation evaluated by a pro, please do not feed these dogs together, or have special toys available where they can provoke a fight.  Dogs will fight over other things, too, but removing the most obvious triggers is a good idea.  Keep in mind that dogs of similar status may fight, even if both are relatively submissive in relationship to another dog in the home.  The caveat about females being more serious when they do fight is correct, however, some dogs do resolve the differences through ritualistic fights, and never draw blood on one another even if they are females.  Also, I am always happier the noisier the dogs are - sometimes that's just "bluster", and the silent ones really can be the deadliest.
You really need to get the situation evaluated by someone familiar with dog behavior.  A vet, or the nearest  college of veterinary medicine can provide a referral.  Or, call the nearest large SPCA.

Also, I am always happier the noisier the dogs are - sometimes that's just "bluster", and the silent ones really can be the deadliest.

 
I completely agree with this.  My girls never make a sound before they lunge.  The looks can sometimes give it away, but only if I'm really focused on it.  Doesn't make for a relaxing environment and my husband has pointed out that my stress level might cause them to react or over-react.  I'm sure he's right, but it's hard to feel carefree when you realize how unpredictable it can be.  I'd say less than 10% of the time have the fights caused any injury, and fortunately, none have been serious, but as you said Sandra, it's hard to believe when you see and hear the fight. 

They make no sounds (growling, etc.) until they are at each other, but then they are very, very loud.
 
I will definately have a behaviorist come for an evaluation before I do anything drastic like give her back to the rescue.  I don't think I could stand the stress if they were to have regular fights with blood drawn.  I think I would return her if I had to keep them seperate all the time- but I hope it doesn't come to that.
 
Anne, its the weirdest thing- they eat about three feet from each other and act quite civil.  I feed them in kind of a triangle and I stand in the middle.  As I put each bowl down I say the dog's name and ask them to sit and then I put the bowl down in front of them.  If someone finishes eating and so much as looks at someone else's bowl I step in front of them and say "own bowl" and they go back to licking their own bowl.  At first I had to hold Zoey back when I put the other dog's bowls down, but now she waits patiently until I say her name and give her her own bowl.  She has been really great at feeding time.
 
After the first episode of resource guarding I made sure to put away the object of the guarding and haven't had any more problems.  Zoey guarded the basket I put all the bones and toys in after I had picked them up.  She doesn't seem to resource guard the bones and toys if they are scattered all over the floor, so I have just resigned myself to never having a tidy house again!  The scuffles that have broken out since that time seem to have no reason (all though I know there is a reason for the dogs, I just can't see it).

The fact that you can't figure out why they are doing it is reason enough to pay a behaviorist.  The possible reasons for dog fights: guarding, sex, food, status, etc.
By any chance, are these dogs about the same age?  And, how old are they?