Well, it's pretty routine for a cat from a shelter to have worms, and you all are good pet parents to make sure she's being treated. But, unless you let her go outside, she probably won't get worms again. Mine never have - although I always take a stool sample in during their annual check-ups. And, if anyone's a little icked out about cleaning the litter til the wormies are gone, you can always wear those little throw-away surgical gloves they sell at Walmart in the vitamin area.
You are a good cat daddy - and maybe you'll have to really keep thanking your mom for her patience and good heart, until she feels too darn 'guilty' to think of returning Maggie!
And, yeah, cats do get spoiled - mine eat better than I do, and get more toys, but when they curl up in bed, waiting for me to join them for a nap, well...it's worth it.