Care Credit is a good option. Here is the link:
CareCredit Healthcare Finance - Payment Plans and Financing for Cosmetic Surgery, Dental, Vision, Hearing, Veterinary & Other Medical Procedures
I really wouldn't wait any longer for her surgery, since those large stones could cause much more devasting and life threatening damage. Her little bladder could puncture or burst, and if she completely blocks up, she could quickly become poisoned from her own toxins. I know finances are an issue for a lot of people right now, but please check into Care Credit or something similar to get that little girl the relief she needs. Good luck to you and keep us posted.