FIRST - call her regular vet and ask about payment plans and reduced fees, you would be surprised at how many vets will work with clients if they just ask.
SECOND - if the vet says no, ask around...
THIRD - contact the local humane society and without revealing too much about WHO you are discussing, find out if they have any programs.
I would hesitate to treat the cat without a scraping to determine exactly what is going on...once you find out, then ask the vet if an over the counter treatment is acceptable.
Please dont be afraid to ask. If you dont ask you dont get.
Case in point, my clients have a dirt poor neighbor whose dog was bleeding out of a puncture wound which had abcessed, blood and yech everywhere and the owners flipping out. Not only were they able to find a neighbor to assist with transporting their dog (they have no car) but they spoke with the vet, who reduced the fee from over four hundred dollars to a bit over a hundred dollars, and another neighbor found out what was going on and covered the bill completely....I have had loads of work done on my dog at reduced fees. There is even a credit card specifically designed for vet, medical and dental care...good luck

There are a lot of resources for seniors and disabled people. Just do a google search on "low income veterinary care."

Here are a few. There are also some listed by area.

http://www.angels4animals.org/programs.html

http://www.fveap.org/sys-tmpl/door/

http://www.companionanimalfoundation.org/

http://www.samsimonfoundation.com/share/docs/files/AdditionalResources.pdf

http://www.hsus.org/pets/pet_care/what_you_can_do_if_you_are_having_trouble_affording_veterinary_care.html