It could be that she hasn't, and just assumed one as an adult. Or something happened to/with her human mother that made her choose another name.

Re: the possible sisters, one of the ideas I'm toying with is that while Brand herself is a healthy woman and can channel the ability to burn with her hands at her wish, I think it's entirely possible other hybrids between her father's species and humanity might not have been so lucky. Maybe I'm Farscape-influenced, but if she had sisters, they could easily have gotten not such a successful genetic combination and died young and painfully. Hence the tatts.