Take her to the vet ASAP. My mother in law's cat had to be put down for that very reason, hopefully the vet can help your cat to pass it but take her in asap.
My Cat Can't Seem To Poop. There Is A Large Bowel That Seems To Be Close To Her Rectum, And It Is Too Big For Her To Get Out. How Can I Help Her?
Your cat may have 'megacolon', a very serious situation that can lead to death if not corrected. Your vet may give her an enema and place her on 'lactulose' to help keep her stool soft and passable. Under certain situations, surgery is needed. My 13-year old cat had this problem; we dealt with it for several months, but eventually had to have him put down. PLEASE SEE A VET ASAP.