KassyG, I'm no expert (my 2 cats got "caught" on exactly the same day; THAT never happened again!).
Check under her belly and see if you notice her nipples getting pronounced and just to generally see if her tummy is getting bigger.
If she is pregnant, you've got about 4 more weeks to get ready (not much you can do).
I also want to ask you to maybe think about getting her nuetered after she delivers this litter. It's really a responsible thing for pet owners/lovers to do. Please don't feel that it would make your cat sad or anything. My vet told me that cats don't have those same maternal feelings that humans do. They have the instinct to know what to do when they have kittens, but there aren't those emotional, gooshy, loving feelings that I know your mom has for you. Maybe you should talk it over with your folks.