Cat Skinny and losing hair and vomiting?

My cat is skinny, losing her hair and vomiting. She is having regular bowel movements and urinating ok. Tried worming, hair ball treatment but nothing worked. She is never allowed outside but one time she did get out because I was trying to shoo away another cat that was antagonizing her through the patio door. She and this cat immediatly fought. My cat has no claws and it was hard to get this other cat away. The other cat bit her and scratched her. This was about 3 months ago. My cat lays around alot more than usual. She is about 4-5 yrs. old. She does not act like she is in any pain. Anyone have any ideas? Her skin is just hanging off her belly and her hair looks awful but not like mange or anything like that. Just thinning out. Oh I have also tried several different food thinking she might have been allergic to the food. But nothing has helped or changed anything.
I adopted her from the pound about 3 yrs. ago. She has not had any shots since then because I was stupid enough to think that since she was inside all the time, I should not have to worry. Her bite was not a big one and scratches were not that bad either. They did not get infected. I put peroxide on them.
I have been afraid to take her to the Vet because I am thinking he will say to put her down. If so I have learned a big lesson. If you keep your cat inside all the time accidents still happen and they still need their shots updated. Poor Oreo and now I am going to have to explain this too my 4yr old special needs little boy who just adores her. I hate to admit it that money is an issue when you have a special child to take care of too. I know, you don’t have the money to take cat to Vet, you should not have the cat. 🙁 🙁

Frankly, I think you need to go to the vet.
It could be signs of feline leukemia (sorry), or an other kind of less dangerous illness, but your cats symptoms are pretty serious. Don’t let it go worse.

It’s true vets are pretty expensive, and for an indoor cat I would not do vaccines either, also because it’s pretty controversial – no need to feel guilty about it.

Maybe you can explain to your child that the cat is very sick, so there will be less to explain in case the worse happens. Children have to learn one day about life and death. It’s tough but necessary.