The reason for the poop change is maybe the organs are beginning to shut down. When she quits peeing in the box it may be time for the ultimate.
Our 16 yr old female (Alvin) got real scrawny/did not take care of herself/I found no evidence of urine in the litter box but she drank a lot of water.
When we took her to the vet for put-down she thought Alvin might have had a thyroid problem. She went very peacefully and then went to Petland for cremation/group burial.
It would be a good idea to keep a close eye on your baby.
Salli