She is very cute, but don't believe everything shelters tell you. Many shelter employees can't tell the difference between a doberman pinscher and a pug... not a big deal since generally shelter employees love animals, but their breed knowledge isn't always up to par.
She looks like a purebred mini pinscher to me, they probably just mislabeled her. Either way, she's adorable and very lucky to have found a wonderful home
I have to agree I think she looks like a purebred Min Pin. It's just that sometimes shelters don't want to be yelled at if a dog isn't really pure, so they'll say mix even if they think it's a purebred. This is the sort of dog a DNA test would probably be worth it if you're that curious, because her results will likely be majority or all Min Pin.