Maesfen
Extremely Old Nag!
I don't think a brindle gene has yet been identified/sequenced so nothing has really been proven.
I think there has, not sure if Sallyf on here from Groomsbridge Stud doesn't have a brindle mare or at least knows of one. If you look in the breeding forum you might find about it.
As I said in Vet, if she or her skin aren't distressed by it leave well alone and accept she's special.