Both Willow and Jessies_mom had really good suggestions. The first thing *I* thot of was catching a sample just to LOOK at it and sniff it. If she's not going often, and it's a uti, then it's going to be dark, smelly and strong and you *may* see blood or flecks in it. VET ... NOW.
Re a UTI -- some dogs will drink TONS to dilute it so it doesn't burn as bad, other dogs will drink less and go less because it burns -- it's a personality thing.
You won't cause pain by 'pressing' with a uti -- now, if the bladder or kidneys are infected THAT could cause pain.
BUT at the same time, I'd also wonder if the position to squat to pee isn't painful because of arthritis. BUT if she avoids going, she could *cause* a UTI by holding it too long.
I think I've told you to try this before -- maybe not. Get her in front of you -- either standing or lying down. Hold your hand out flat -- and very slowly pass your hand over her spine from the top of her head to her butt, almost but not quite touching her. Leave a tiny airspace (she's fluffy so touching the coat is fine -- just don't have your hand close enough to rest on her skin).
But feel for hot areas or cold areas. Take your time -- really concentrate and try only to feel for hot or cold air under your hand. If there is an inflamed area -- you *will* likely feel it. It's kind of amazing.
Then go further -- down her legs, near her knees, ankles -- and then see if you can get her to roll over a bit and see if you feel anything abnormally warm (or cool) over the abdomen, inside of the groin/legs, etc.
Just trying to find inflammation or cold (cold is areas where there may be a lack of circulation -- lack of adequate blood flow because some area nearby may be too warm). It can sometimes help you to find soreness you wouldn't otherwise find.
A fish bone could be problematic -- it could have punctured something or caused bleeding. (make sure you check her poop -- if it's abnormally dark, or black -- again, that's a "vet NOW" thing).
If you have a drug/grocery store nearby get a bottle of green alcohol. It's got wintergreen oil in it and it's cheap. Use that to massage places like knees, hips, lower back or any place you suspect is uncomfortable. The more you rub the more heat you'll create with the oil. It won't hurt, might help a lot. And if she improves after a massage it WILL tell you something.
Get her to the vet as soon as you can tho -- it's warranted. But how much of an emergency? You'll have to judge that. But looking at a caught urine sample -- if you look at it and say "YUCK -- I can't even get close to it because it's soooooo stinky!" -- that's a dog that needs a vet a.s.a.p. If there is blood -- vet NOW.
But it's those little things that tell you she's "off" -- that's the best reason to take her to the vet -- do it as quick as you can, but don't strip a gear.
One more test -- do you know how to test the "capillary refill" time? Lift her lip and see if her lips are pink. Now if she has dark spots on her gums that may be hard, but still -- I've seen dogs with dark gums that are "pale" under the darkness. That's bad.
Their gums should be the color of ours. Pink. But in any event -- take the tip of your finger and press hard on the gum for about 10 seconds. Release -- does the color snap right back to pink? Or does it take a few seconds to return to colr? If so that's BAD -- VET NOW.
If the gum is just plain "pale" -- VET NOW. Those are all tests for anemia or potential internal bleeding -- for some reason if their gums are abnormally pale -- that's dangerous.