I have an elderly Labrador bitch which used to belong to my ex H really but when we split, he couldn't take her and the children and I were so very fond of her that we took her with us. She is now 13 years old and the vet thinks that she has some kind of uterine infection as she is constantly vomiting going on antibiotics, better for a two or three weeks then starts vomiting again. In between all this, as she is also very arthritic and is on Loxicam which she has to stop taking when she is on the antibiotics, she becomes stiffer then has to go onto tramadol while we get the Loxicam up and running again and so it goes round and round in circles.
Our vet wants to spay her as she is still entire. History behind this is that Ex H got her from a friend and wanted to breed from her but, when it came to it, her hip score wasn't good enough. I know she should have been spayed then but she was, "his dog" and he was too tight unwilling to spend the money. 
Now, there is no way that I can afford the operation. Our vet, who knows the situation, has already been very kind and lenient with the bills, which don't always get paid in accordance to their, "payment required at time of treatment" policy. I am on a very low income and just can't afford the operation all the time the other treatments are ongoing as I am always playing, "catch up" with the vets fees and can't save. (There is no question of being able to cough up £500 out of one month's income and the bank won't give me a loan because of my low income)
It seems to me that, for her sake and ours, I will have to look at the vet putting her to sleep but this is a very sad thought as she is such a sweet old thing and very loving and we all love her very much. If she were younger, I would think about trying to re-home her but, 1) Would that be too stressful for her after 13 years with us and, 2) Would anyone take such an old dog needing so much spent on her?
Any advice would be appreciated, or just someone to hold my hand while we go through this.
Thank you.