Help Kitty Poop...please...

have a large female cat,started hunching up like it has to go to the
bathroom,went online figured it was alot of hairballs in her,went to petmeds
and bought laxatone for
hairball elimination,when she does poop they are thin poops and have much
hair in them,but i guess what i think
is happening now is that she is dehydrated,and the poop must be rock hard in
her......
is there something i can buy ,or give her to help her poop soften up so she
can go alittle easier?

thanks for any help
Dan