Actually, the last page suggests that it IS Bra throughout. Bra never has her hair styled in the way that Bulma does once she gets older. And I doubt Bulma could go from ponytail to that other style in the space of one page.
It's a rewrite. In the original, Bulma asked the dragon to become younger (she commented about that at the end of DBZ when Goku told her that she is an old woman now).