Although Stephenie Meyer didn't include any gay people in her canon (Maggie is canon, but no remarks whatever are made of her romantic inclinations), she has said that gay humans turn into gay vampires. Also, the whole "mystical bond" thing is never spelled out in so many words in canon, although it is blatantly obvious anyway - it's characterized as simply falling in love. So I decided Maggie's going to be gay in Luminosity, and given that she's aware of this, she has excellent reason to expect her mate to be a girl.