I really don't think it's his mother. Cyrus' hair originally isn't white. It turned white while he was kept in "hibernation" or whatever. This just indicates, along with the "ancient" stuff in the room , that she is most likely from the same time period as Cyrus (give or take a year), and they are in similar shoes.(The girl is also young, i don't think "hibernation" can reverse your age, but it sure can "freeze" it) I think it's either Diana under a different name for whatever reason (due to the hairstyle and the plants), or a new character entirely (perhaps related to her?).