Im so sorry to hear your dear kitty is having a problem, I wonder if you are able to upload a photo of this on your profile page?
this could be a boil/cyst as the others have mentioned, I don't want to scare you but it could also be cancerous....any lump or growth on an animal has to be investigated.
In the US there is the option of a care credit card to help pay for Vet expenses when you are in financial difficulty. it would be worth applying for, but as all credit it does have to be paid back, but you do have the option of paying on a monthly basis.
Also call all the clinics in your area and ask if one of them would consider seeing the kitty and giving an opinion, tell them your situation and hopefully one will allow a payment to be done monthly as well....good luck♥
http://www.carecredit.com/
Do you know if she has been bitten by another cat? Could be an abscess.
Here in UK we have vets for people who cannot afford the usual vet. We just pay a donation. What we can afford. It is called The People's Dispensary For Sick Animals (PDSA). Do you have anything like that where you live?
it might be a cyst or a blister i would take her to the vet you can call your local shelter and ask them for the names of free or cheap vets for someone who is on disability and they will see her for little or no cost