It's important to note that crystalluria (crystals in the urine) is usually clinical insignificant but can be important in limited situations. For example, crystal type is important in association with current or prior occurrence of calculi (stones) and when one suspects a portosystemic shunt (vascular abnormality associated with the liver), ethylene glycol toxicity, or melamine intoxication. Whenever crystalluria is considered significant, it's important to examine fresh, unrefrigerated urine specimens and the urine pH should be assessed within an hour of urine collection.
Crystalluria often causes concerns about urolithiasis (stones in the urine) but animals with crystalluria don't necessarily form uroliths and finding crystalluria is not an indication for treatment. For example, dogs normally excrete a large amount of ammonium magnesium phosphate (struvite). With urine pH greater than 6.5, this normal excretion begins to become visible as struvite crystals. The higher the pH, the more crystals become evident. Struvite crystalluria is normal in most dogs. Urolithiasis becomes a risk when urine pH remains consistently alkaline, usually from infection with urease-producing bacteria.
Rather than diet, then, rigorous control of infection in Paisley makes more sense to me. Because she presents with clinical signs of a UTI so often, please consider having regular urinalyses performed every 3 months in order to ensure that her urine is staying sterile which then should keep her urine pH lower. Please note, too, that neither cranberry nor lemon is expected to be helpful. The use of those foods has not been shown to be reliably effective in the urinary tract of dogs.
Please respond with further questions or concerns if you wish.