My great-great granddaughter wants to her child a stupid name?

My great-great granddaughter is pregnant and she wants to give the child an "African-American" name (even though there is no such thing) because the father is black. The father's name is DeShawn and she wants to name is LiShawn if it's a boy and DeShawna if it's a girl so it can have a "heritage." Her G-G-Grandfather (my husband) was Maasai and I offered some of those names but she doesn't want those because those are "boring." She's very young (15) so she doesn't know that you can literally ruin a child's life by giving them a name like that (who was the last DeShawna to graduate from Harvard?). I'm the one who is going to be raising her her and her child for the next decade while she finishes school and college. I think the least she can do for me is honor this one wish to give the child a good name. How can I convince her? Can I legally go over her head or something? I'm sorry but I'm not having a DeShawna/LiShawn in my family. She won't even settle for just naming them Shawn/Shawna. Even worse are the middle names (Candy, Rock, Sweet, Blue are some examples).