My dog farts a lot?

My dog is a pitbull and English bulldog mix. She has a crate in the living room and whenever she's in it and I walk by, there's always a foul fart in the air. It smells so bad. Right now she's in my room laying on the floor and every 10 minutes or so she farts again and is lighting up my entire room. She's been eating the same dog food for months but occasionally she sneaks some of my cat's food, so maybe that could be the problem. I just don't know what to do and I love her to death but I cannot stand the smell.