Choppers sick

I have two boxers, Chopper who is 10 1/2 and Jaws who is 9 (around 9 is the end of a boxers life span typically). The past week and a half Chopper has dropped too much weight. She has been eating barely anything at all and for the past few days nothing. She drinks like a camel as if there will never be any water ever again and then throws it right back up. I have tried putting chicken and beef broth on her food which only works a little, in the past she would have devoured the entire bowl of food that was soaked with people food. So shes not eating, dropped a ton of weight, drinking and eating her pee and poop and had the shivers. All this while Jaws is fine. I got her in the the vet today, she has a huge cyst in her uterus.

If female dogs are not spayed before their first menstruation there is a risk of them developing cysts in their uterus and this risk gets higher with every passing menstruation. My vet has given me this info and told me about this possibility in the past, I have some guilt over this situation as it could have been prevented-somewhat, she would have had to still have surgery to spay her, but she wouldn't have gotten so sick first. I couldn't afford it then, and now, I still can't afford it. I don't know how I'm going to pay for this, I'm maxed out on credit cards and there's no extra cash right now. What are my options, put her to sleep or give her the surgery and hope they will let me pay in payments??

I opted for surgery of course, how could I possible put a dog to sleep on purpose when something is curable, shes my baby a part of my family. I cried so much today I have a migraine and my eyes hurt. She's at the vet's over night on an IV and will have surgery in the morning. I have an excellent vet and I have very high hopes that Chopper will come through this ok. There is of course the chance of problems, but the cyst has not burst so that alone increases the chances of a good outcome. Surgery starts around 7:30-8 tomorrow and they'll call me around 10am. I'm a nervous wreck, I feel like I'm going to throw up.