Lux is not in any danger. Some members of her family, Garen included, already know she's a mage, its even a fear of both of them (listen to their interactions with the scarecrow champion, Fiddlesticks). Her aunt is Tianna Crownguard, the highest military general, and Tianna's husband is the leader of the Mageseekers
Lux does not like the Mageseekers, obviously, and wants them to stop, but she doesn't want to slaughter them all like Sylas wants to. She's not Sylas' friend (anymore, at least), and she's definitely not willing to have a romantic relationship with him.