Neighborhood Cat - worms or post pregnancy hunger?

I have a neighborhood cat that I've been feeding for about a month.  I see her every morning and sometimes in the evening.  When she first started coming up she was pregnant but somewhere in there she had kittens.  She doesn't live around my house but lives about a block down the street (followed her home one day) so I really don't know her habits, where she poops, etc.  My question is if she is staying so skinny due to nursing or could she have worms?  If it is worms is there anything I can put out for her (like the powder for fleas).  I just don't have the money right now to take her to the vet.  I've just taken two and the costs are getting more than I have.  I called several local rescues for help but they told me they had just too many cats/kittens right now and couldn't take any more. 

She is eating one whole can of Friskees in the morning and a couple bites of dried food and then comes back about 30 minutes later wanting more.  I feed three other cats and if I time it wrong she will eat their food too!  I know she really needs to go to the vet but I just can't spend the money right now.  I have another cat that I have an appointment for on the 25th that I'm trying to get spayed and shots for.  Managing these neighborhood cats is getting a little expensive!!

I would say if she's nursing, she should definately be eating much more than normal, but honesty I don't know much about nursing cats since I've never had one.  PLUS I've never had a cat that needed deworming or flea treatment, but always read they they need either the treatment between the shoulders blades (like Advantage or REvolution) or pills for worms, or both.  BUT doesn't she belong to someone?.  Not sure how legal it is for you to give actual treatment to someone else's cat in the first place.  Feeding is one thing, but actual treatment might get you in trouble...not sure.  What if they know she can't tolerate certain things? 

Thanks for reply MrsGreenJeens!

I just followed her home and low and behold there were six kittens sitting on the porch.  They were not afraid of me so they are being handled.  I tried knocking on the door but no one answered.  I wanted to see if they are just feeding them or are taking care of them too.  If not I plan to offer to take her over to get spayed and dewormed.  The kittens were eating dry food so they must be weaned.  That's one hurdle!

I would still like to get her spayed and make sure she doesn't have worms.  She is eating so much I just worry.  Once I know she has a place to stay after being spayed I'll offer to take care of it. 

There are about 10-15 cats on this street and I don't want her turning into a baby machine!

Yes, getting her spayed would be a GREAT thing!