Tenderwing never met her mother.
After encountering a ghostly knight at Whitewing Castle, she was possessed and ridden by his spirit. Now she is bound, in some kind of way, to the Shimmering Queen that rules that accursed castle. Her personality and the spirit's have merged somewhat, in a way that deeply frightens Tenderwing.
Tenderwing uses pact magic. This means that, basically, her magic doesn't work unless she has a pact with someone that says it does. That's okay though, because she's always making minor pacts with mortals to tie them to her.