I spoke too soon. She had that one semi-normal poo, then it's all been bad since then. I'm calling the vet in the morning to make an appointment to bring her in to make sure she isn't ill and I'll talk to her about allergies as well.Just a wee update on the kitty - things were better this morning! Shaped more like it should be (still softish, but at least it had the proper form) and she did it without stinking up the whole apartment/waking us up. Her behind is clean. All I did was skip the pumpkin last night. I'm cautiously optimistic.
Thanks, all, for the replies.
It occurred to me that I switched her cat litter from a cheap clay litter to Swheat Scoop wheat litter about the same time I started giving her canned food in the evening. In case she has become allergic to it, I think I'm going to switch her litter to a more standard quality clay litter. I also think I'm going to change her food (again!) to grain-free. Just in case..