PH can change at different times during the day.... I have tested with strips myself and seen this. Also, if the urine sample sits a while, struvite crystals can form - fresh samples is always best. Vit c - makes the urine more acidic, breaking down the struvite crystals(to bowel tolerance). Just the presence of struvite crystals doesn't mean there is a UTI going on -But they can cause a UTI. Was there blood and bacterta in the urine to confirm a UTI?
Sometimes a sterile sample is best if there is questions and then a culture to see what would work best as an antibiotic-if needed.

Best wishes for the girl. Some answers will give some comfort rather than alarm.

I use them too. The best time to test urine is first thHing in the a.m. prior to food or water and in mid stream.

An elevated PH can be an indication of UTI as well as struvites.

A cystosentesis for pure sample is best for doing a culture/sensitivity to pinpoint the type of bacteria for proper meds.

Wondering if the pet owner noticed any symptoms of UTI: frequent squatting, leaking while sleeping, accidents in the house.

Hoping they get on the right meds and clear this up.

No, it doesn't sound fishy to me. The dog is at that age where these things are more common. I doubt the vet lied about the presence of crystals. If left untreated crystals can form into stones and this can result in a life threatening condition. Is the dog going out often enough to potty? Less frequent trips outside can help encourage crystal formation. Is the dog drinking enough? Has there been a diet change? More plant based foods cause alkalinity, meat based foods help with acidity. Too many fruit and veggie treats can throw the balance off, better to add a little canned food instead. A food change might help especially if the owner is adding stuff to make the dog food work.