Hello and welcome back.
I am so sorry your girl is having this problem.
Unfortunately SD is rejected by a lot of cats. There are several other brands of urinary diet, you may want to see if your vet can get purina UR as cats tend to like this much better.
Until you can get a different food she has to eat. Not eating in cats can cause liver damage. I would feed what ever food she was eating before the switch. A day or two of her old diet will cause less risks to her health the not eating.
Call your vet first thing Monday and let them know what has transpired over the weekend.
Please reply back if I can be of additional assistance.
Best wishes. Candy
Veterinary Assistant
Practicing Veterinary Technician for 23 years. Veterinary Practice Owner, Technician Trainer