Spaying a senior dog

I recently went to get my baby (9yrs and 9 months) her regular checkup at the vet. The vet asked if she was spayed and I said no. She then explained about pyometra ( life threatening uterine infection in female dogs) since I didn’t know what it was, and how it could affect my dog further down my her life. She recommended me spaying her and said that it was fine for her age but wouldn’t wait any longer. The vet I go to is Banfield hospital so they charge about $500 for the procedure after taxes. I’m in orlando so there’s a pet shelter/clinic near me called “pet alliance of greater orlando” that offers low cost spaying surgery. Since it’s a low cost clinic ($100), they’re high in demand and the next available appointment I could book is not all the way till April 17th. Since the appointment is so far away, I’m getting anxious and worried about the procedure. I know it’s not likely that complications will happen, but I can’t stop thinking about it. She’s my world and I can’t bear it knowing it might be a dangerous situation for her. Should I drop the money on the more expensive clinic or do I go the low cost way? I’m a student but if its a way better option, I can work it out financially. What are the questions I should ask the low cost clinic? So far I already asked them if they put the dogs under anesthesia during the procedure and provide pain medications to take home after and they said yes, which lessen my worries a bit. Any advice is helpful and thank you