Fleas are driving me mad, difficult situation as cat is technically not ours.

So we have had a cat that has visited us ever since we moved into our house, she wont go back to her original home, iv tried over and over to get her home but she wont go. Spoke to her original owner who was not that bothered and i think has given up on her coming home. I know she comes to us a lot but i also think she visits other houses as she does sometimes disappear for a few days at a time.

Her flea treatment has obviously run out and she's picked up fleas, i have given her a few of the 24hr tablets but they keep coming back. I don't want to give her frontline or advance as theres a chance she goes to someone else's house and they give it her too which could be dangerous, but at the same time i want to get rid of these fleas. Natural rememdies online seem to be conflicting. I also cant rid them from my house until they're gone from her and vice versa. Iv tried sprinkling salt everywhere and had thought it worked however i just had a flea jump on me so obviously not. I feel so itchy and paranoid, i just want them out!

I don't think there is anything you can do unless you take ownership of this cat and keep her indoors, unfortunately.  You are right to be concerned and there isn't a solution I can think of.

To at least rid house of fleas you can use diatomaceous earth it is cheap. You can get a bag at Lowes or Home Depot. I've used it and just be very diligent about vacuuming this should take care of the fleas.

what I would do is  apply frontline or advantage and put a collar on her that is safe for cats and put a tag on the collar stating last day of flea treatment and what you used, if the cat comes back with out the collar put another one on her with another tag stating the same thing if that happens again I would just keep the cat as yours and keep her indoors and have her seen by a vet and fixed if she isn't already obviously the other owners dont really care about her

you know thous tags that is plastic with paper in it to wright on? buy thous they are cheap I think they are in the auto part department of walmart