I'm so sorry you're feeling guilty about this, and I do understand. I felt horribly guilty when I purchased my show puppy a few years ago

I'd wager you're doing a great job taking care of your cat. Cats tend to let you know if they're not happy, and if your cat is wanting attention from you, then it's probably totally happy. Sometimes, it's okay to be selfish for things you want, like a pet. The cat is getting something out of this too - a safe, loving home. If you hadn't adopted her, or if you were to return her, there is a very, very good chance that she'd be put down. You've saved her live, and you get the companionship of your cat in return. Cats and dogs are COMPANION animals - it's their purpose to keep people happy. If you're enjoying her company, then you're both doing something right.

I think you're getting in to some core belief stuff here - these beliefs that you're un-likeable or undeserving of affection. Cats are easy - if they like you, they show affection, if they don't like you, they won't come near you. The thing with animals is, they're very uncomplicated in this regard. There are no hidden motives, no lying, no eggshells to walk on. If you provide for the animal and show it affection, you will get affection in return. I think pets are a great way to practice accepting affection and accepting that you're not as horrible of a person as you might think. (At least it has been for me...)

Enjoy your cat, do the best you can, and accept the comfort she can offer you!

Oh - and on the subject of tapeworms...it takes a minimum of 21 days before you start to see tapeworm segments externally. So, she probably had them before coming to you. Treat her and she'll be fine. I've often had foster dogs come in with tapes - it's just kind of a given that a dog or cat from a shelter will have them. I've even had my own dogs get them a time or two - usually after catching and killing a bunny or squirrel or some other critter.