A cat isn't as dependent as a dog. They don't need to be walked and they're very clean. They are usually happy just playing by themselves but they still need to feel loved. And watch out for your mom's houseplants. They love to eat them.
Birds are pretty easy to take care of.
They live happily in cages. Birds can be kind of jumpy so you have to be gentle with them. They love to be whistled to. If you have a bird you will have to clean their cage about once a week and you'll be sweeping up a lot of seed off the floor. Fish make good pets.