I think Mia Love would have been the best choice. She serves the same role as Pence, which is to tie him to the traditional Republican base; in addition, she as a former critic of his, particularly his comments on race, if she were to join the ticket it would tremendously shore up his defenses in that area. As an African-American, she appeals to the most influential voting-minority in the country. Alas, it is only a dream...
You could argue that she’s African-American lite in the same way Barack is (both are the children of immigrants, both of their “blackness” has been questioned on idpol/cultural grounds), but that wouldn’t have mattered to Trump’s primary base.