Crystals are not something to tinker with -- they indicate she is developing stones. Get her on the prescription food asap. Use the Royal Canin one, NOT the Science Diet one. If your vet only offers the Science Diet one, get the script from him and get the Royal Canin food elsewhere.

Once the crystals are clear, you can try returning to another food. You can take in a urine sample once a month to test for crystals. If those appear again, then go back on the prescription food till they clear up.

Bichons are prone to bladder stones. Thank goodness I have never had to deal with them. So many on the bichon forum have. My friend just 17 miles from me, her Mattie has had surgery to remove bladder stones THREE times in 18 months. The first time, after the surgery, my friend tried doing online research and preparing food herself. That didn't work. The second time, she did not have the urine tested regularly, but skipped a month and in fact crystals had started forming. Now she regularly takes in a urine sample each month -- it is easier and less costly than the surgery.