Caretaker is way better. “I’ll put a black woman in as a placeholder until a real senator can be elected” sounds horrible.
I mean, it’s a very pro-democracy move to make an explicitly temporary appointment and not distort the election. It’s also a very progressive move to fill the seat with a highly qualified member of an under-represented group. High marks on both counts. It’s just hard to describe the coincidence of those goals in a way that doesn’t sound like tokenism.