Stinky poop?

Nick was complaining about the smell of the litter box after Onyx used it, so I went to go cover her poop for her (she doesn't always do it herself), and I noticed that it was a very soft pile, very stinky. It's normally a fairly firm sort of little log, like all the kitty poop I've seen. She hasn't had any changes in food lately, so I'm not really sure what could have caused the change. Any thoughts?
(No changes in personality or activity either, if that helps. She's very active and playful.)

Is it always that stinky?

It's always a little stinky (probably just because she doesn't cover it), but it's not usually this strong.
And as I said, it's very soft. Not quite diarrhea, but much mushier than normal.

What brands are you feeding her?

You can mix a tablespoon of pumpkin in with wet food daily to help with both soft stools and constipation. My cats both get pumpkin daily. You might also want to add a probiotic if this persists. 

Both my girls eat Nature's Variety Instincts Raw Boost dry food, duck and Turkey flavor.
I've tried giving her wet food as a treat, I'd like to switch them when I can, but she didn't seem to recognize that it's food. I offered it to her a few times, but she just sniffed it and walked away.
I'll give pumpkin a try by itself (she likes odd things so she might eat it by itself) and keep an eye on the litter box.

Soft, smelly poop is usually indicative of food intolerance.  If this is a newer food, it might be a little bit too rich for her.

She's been eating this food as long as we've had her. Granted, that's only about four weeks, but this is the first time her poop has been anything other than normal.