Fleas cause tapeworm and the worms eat a lot of the food that you feed your kitty.
There are medicines that you put on the skin at the back of her neck, a small amount. However, you can only get them at a vet office.
If you can find a vet that will take a payment plan, or if there is a vet school somewhere near you, please get your kitty in. If she is an indoor/outdoor cat, she will need the med once a month.
Is she spayed?
"You can say any foolish thing to a dog, and the dog will give you a look that says, 'Wow, you're right! I never would've thought of that!'" -- Dave Barry