Long haired dogs can be brindle color, but they look more mottled or patchy because the stripes appears less well defined. Don't get too wrapped up with what the shelter listed as her mix. They are just making a best guess unless they have solid information as to the parents. Shelters sometimes list dogs (not entirely honestly) based on what will generate some interest in adoptions. In my area, there are dozens (if not hundreds) of "Lab mix", "terrier mix", "Boxer mix", and "[other] mix" dogs for adoption. They almost all look surprisingly like Pit Bulls or Pit mixes. I've seen more than a few listings that were LMAO funny.