I would definately take her in to the vet. If it is hard there is a chance the bowel is now protruding and it could cause the bowel to die (incarceration). Then you will really have a problem. Here is a site that will loan money for pet care at a lower rate
http://www.carecredit.com/ . If you plan on spaying her you can have it fixed at the same time and save some money.
But at least have it looked at...