Depends on the type of crystals. You need to find out from the vet, she either has struvite or oxylate. Struvite are a sign of alkeline urine, high ph.......oxylate mean she's very acidic. How bad were the crystals? Does she have a lot of them? A change in diet can go a long way to keeping them under control.
If she has struvite there's a medication call methiaform that will acidify, please think twice about putting her on a "prescirption" food, it's crap and is basically medicated with the methiaform. It's better too feed a better food and give the pill.
You can lower ph with food, cranberries, blueberries, acidic fruit. It doesn't take much. What are you feeding her for her regular diet?
If she has oxylate crystals you can make her more alkeline with dark leafy greens, collard greens, mustard greens, kale, chard, beet and carrot tops. A fresh diet can help enormously with crystal issues. Some breeds are prone to crystals, pugs, and need to medicated. Good luck.