Provded she's smart enough to clean beforehand then no it's unlikely, but you do get the situation where you both want it and it's not attractive for her to go BRB NEED TO TAKE A SHIT FIRST, cause it's kind of a mood killer.
In my experience with women it's never smelt, but i don't really take in an air full of her asshole or smell my dick afterwards.
You wouldn't really be focusing on the smell in retrospect, but i can see why you'd ask that.
Just be hygenic and if necessary put scented candles in the room or something?
Like i said, never had that issue with my ex but every person is different.