It sounds like either worms or coccidia, a single-celled intestinal parasite. My kittens had that and one had bad problems with bloating and a little diarrhea. These parasites will show up in a fecal float test which is pretty inexpensive. Just bring a fresh fecal sample to a vet and they'll do the test. It's only $15 at my vet's office. The test plus meds for both kittens was only $25.
If Mom has intestinal parasites, so do the kittens. You should get them treated too.
And like the others I highly recommend getting your cat spayed. Here are some resources to help you look for a low cost clinic:http://neuterspay.org/spay_neuter_re...s_by_state.htmhttp://www.lovethatcat.com/spayneuter.htmlhttp://www.friendsofanimals.org/prog...ter/index.html
And you can call your shelter. Many shelters have their own spay/neuter clinics or can help you find one. My shelter's clinic costs only $30 and I think it has a sliding scale in case you are having serious money issues. Till then, please keep her indoors and away from unneutered male cats. Plus, if she doesn't go outdoors she'll be less likely to pick up more parasites.