what is wrong with my dog

I agree on the dog parks.  My dogs always had each other to play with, but even if they had not, if I had had a single dog, I'm just not comfortable with dog parks.  I have gone with a few of my kids, one at a time, but only in extremely controlled situations and never with more than one other dog there, and it had to be a dog I already knew well. 

Dog parks can be a terrible crap shoot, and losing there can be deadly.  A really safe muzzle isn't safe for a playing dog.  Those can only be left on for a very short time since the dog can't pant, so can't sweat.  I've yet to find a basket muzzle that they can't get off, and I just really don't care for using them.

 The jack russel she was chasing so i imagine it triggered a prey response she was pretending it was a rabbit and grabbed him only her teeth went in. She was not out to kill the russel it wasnt a fight or an attack she just grabbed it when the russel screamed she let go and it was over and she looked confused as to what happend. It was not a fight it was a play time gone wrong or dangerous. There was no aggression there that time she wasnt trying to hurt him. There was a big laberdoodle with them also the 3 of them were bouncing around like goofs and it happend out of the blue.

the doberman and her well they had met before the dobie snapped at her in the past she didnt forget the dobie snapping at her she held a nasty grudge I guess and really wanted to finish him off and kill him for snapping at her.  He wen't for her neck once out of the blue but never bit her just snapped. And she never forgot i guess cause the next time she got a free chance she ran for him and took him out and almost killed him. Everything was normal and then in a split second she just took off after him and took him out. She has NEVER done anything like this. She wont even do that to a goose or a cat or an animal or a deer. SHe never leaves my side like that and just attacks another animal. But she did when she saw that dobie. My trainer said female dogs can hold a nasty grudge and can fight till the death. German shepherds are well known for it.

 the dobie knew exactly who she was when he saw her also

lol she wasnt trying to get even but it was carried on since then i know that if we tried to make our dogs meet again they would end up having to peel my dog off theirs, time won't change the relationship between the 2 dogs she will remember him and he will remember her, if i pass the dobie when hes in a fence he knows who she is. I know the owner now after paying his vet bills I have seen the dobie again in a park he has seen my dog walk by he knows exactly who she is when he cowers in fear when he sees her walk by. Hes terrified of her even after a month goes by. HE is a confidant dog but when i pass his fence the other day to give a msg to his owner he cowered in fear and ran and my dog didnt even do anything as she was focused on me. This dobie is the alpha of his pack and a naturally confidant dog so he had no issues.

I know that there is no way in hell these 2 dogs will ever live together sometimes 2 dogs just can't get along 

Dogs do remember unpleasant encounters and it's not uncommon to see what appears to be retaliatory behavior.  I dislike using that term but I don't know a better way to describe it.  It's most likely a case of a good offense being the best defense.  That's why the more often a dog has a bad interaction, with a particular dog, they might display more severe behavior at the next encounter. 

I agree with the OP about the incident with the JRT.  It sounds like that could have been a chase game that got out of hand.  The size difference between the two may have contributed and predatory drift may have come into play.

Dogs do live in the moment but they also have very good memories when it comes to survival skills. If you've ever owned a dog who had a bad encounter with a particular breed/color/size/shape of dog and then seen your dog react negatively to other dogs with similar looks, it's obvious they've retained a negative impression.  Not saying all dogs react this way but often enough to be something to consider.

heck Jackie, most of the time I don't know what's going on in MY mind.

Generalizations concern me, whether they are about a specific breed of dog, or people.

I agree, yes, it sounds like the jack russel incident was play gone too far, which is why I suggested the she may have very poor bite inhibition.  There could be a number of reasons for that, but the root of the problem won't be found on the internet from any of us, no matter how well meaning we are.

 Stop taking this dog to the dog park unless you want this to become a bigger issue than it already is. Most dogs don't belong in there for one reason or another, and this dog is obviously one of them. Plenty of dogs are perfectly fine without the dog park. Mine only go if it's only them in there.

Dog's can't necessarily hold grudges like humans or want to exact any sort of revenge, but dogs can remember that in previous situations with a particular dog, or a particular type of dog, it has been bad. They can recall that and choose to act before the other dog. Or the dog could have been giving off smaller, less noticeable signals in the past that went unnoticed, thus felt the need to escalate to more noticeable behaviors in order to meet the function (getting away from another dog, or getting it away from himself). It's more likely this is what happens or happened rather than the dog just snapping.

I think you've gotten some good advice/information from others but just want to emphasize that regardless of the how or why of what's happened, you know now that you can no longer trust your dog in a dog park situation. IMO, that won't change with training or a behaviorist. You could set up play dates with dogs that you know and she enjoys playing with. Good luck!

 I just want to chime in (late) that a) dog parks aren't for all dogs- for a variety of reasons.

Yes same-sex aggression exists and is common in mature GSD's especially from working lines

A long time member of this forum that understands the breed especially well has always said that a mature GSD should NOT be a 'good' dog park dog. They shouldn't be super social. Same sex aggression isn't uncommon and certain breeds are definitely more prone to it.

Your dog has matured past the point of it being appropriate for her to be at the dog park. Period