Wren Bennett sounds great. Do characters even need mns? I mean, they wouldn't ever really be given.
Serenity "
Wren" does seem a bit, well, stretched. Wouldn't you spell it
Ren, as there is no w in
Serenity? Wouldn't the more natural nickname be Sair or something? I think
Wren would be fine as a full name for a character.
Or maybe, to make her a bit more realistic,
Wren could be her middle name that she goes by because her first name is too common or formal for her.
Jennifer WrenAshley WrenElizabeth WrenRachel WrenDanielle Wren.. or something?
Good luck :)