They can be passed by direct connection, such as grooming. Worms can be passed on by fleas, so mutual grooming or sharing the same litter tray, or just cats that live in the same household can contract worms.
Actually, both humans and cats can get 'ringworm'. You or someone else who lives with you most likely carried it in on your shoes or clothes. Maybe you even gave it to her! You can get a simple...
Worming is pretty easy, if you're willing to spend a few dollars. Go to your local vet and ask them for worm medication. Sometimes they will ask how much does your cat weigh. Also, it is hard to...