This is not at all a judgment on you OP nor a judgment on all boarding facilities…I’m just going to tell you about my experiences…
I have worked at a number of facilities that offer boarding. I obviously don’t know what yours does/did. But…at the facilities I have worked in and currently work in, boarding dogs either A) only go outside if you pay extra or B) are on a pretty strict schedule–for example, we take dogs out at 6am, around noon, and again around 5:30. Therefore, they often learn to urinate and defecate inside else they hold it until they’re about ready to pop which in the case of urine, CAN set them up for a UTI. Even the place where I take my dog for grooming that offers day care and boarding does not take the dogs outside–EVER. There’s really no place to do it. So I often (every time!) end up with a dog who has some accidents in the house after spending even a day there for grooming.
While a UTI may be the culprit, it may also be that she kind of got in the habit of going inside because that was her only option.
For this reason, I tend to not board my dogs. I can’t much avoid the grooming situation because I don’t have a good place to do it myself since our move. But I simply do not board my dogs. I pay someone to stay with them at the house and maintain the usual schedule.
In your situation, you could do a free catch of a urine sample and take that in to your vet if you think it could be a UTI, else you could just give it a few more days and really stick to the schedule.
This may not be a dog who handles the boarding situation well. Hard to say. I’m not saying that she’s not HAPPY where you boarded, but she may well think “oh, we’re doing the inside potty thing again. Okay!”