Wow, that's one terrible looking eye, and it's been untreated for a long time. She needs to see a vet immediately. You should be able to find a vet for an initial evaluation for 30-50 bucks. Then they can give you an idea of treatment or likely removal costs.
If you can't afford an evaluation...
Yupp not new to pillow stealing here. Ashley has to sleep on a pillow on the bed at night. If she doesn't get her own pillow she'll try to sleep right on your head!
One of my cats had a lump that looked like that (though smaller) on her tail, and it turned out to be a fluid cyst. They were able to drain most of it with a needle, and the antibiotics took care of what was left.
So that would be my guess... Hope it's nothing serious
Cats can get heartworms just like dogs. Though cats are much more resistant to them than dogs, it can happen.
Prevention is the same as dogs, a monthly tablet.
Antifreeze is very toxic, it takes only tiny amounts indigested to kill. I lost my Grendel cat to antifreeze. If it's allready on the ground mop up what you can, and hose the rest down to dilute it as much as possible.
Cat litter will attract cats so I would not put litter on it.