You'd wouldn't actually get your knee that high up and your kicking foot that far back if you were actually doing this pose. Her body would have to be in a Y shape for that to even be close to possible and even then the lower leg would still not be as far back as this image has it.
As of now, we have no idea about her physical appearance, but Toriyama gave away some bits of info about her character very recently (check references below): she was a singer named Miguel who died shortly after Videl was born.
i like to imagine if she self-destructed while not audibly saying shes going to, she'd kill those two because they both tend to get in close range for whatever reason despite having ranged guns built into their weapons.