She could easily be a pure bred Pit Bull. There are a number of people who compete in weight pull with tiny Pit Bulls, I believe Missy's dogs are in the low to mid 30 pound range, and Soleil isn't much larger than that either. So a small dog of one of those litters could be 28 pounds full grown - or under weight or under muscle.
I agree with Suzanne, Patterdales are pretty rare so a mix would be a long shot. If there was white on her I would say maybe a JRT mix if anything. We're so conditioned to seeing the oversized ones now that the correct sizes look weird. 28 pounds is really only a touch under the small end of the standard.
Riggs is 45-47 pounds when he's at correct weight, though I've been told he looks bigger in pictures, measurement wise he's pretty little.
Inside me is a thin woman trying to get out. I usually shut the bitch up with a martini.