I would say brown or dark bay. Definitely not black. The light color in her tail could be bleaching from the sun or probably a trait she inherited from her sire. Many tobianos have 2-toned manes & tails.
I'm inclined to say she's a seal brown, she has the light colouring on the inside off her legs, her flanks, her muzzle and around her eye. The tail is getting me though. Could just be a random mutation, something curious though! :).