Elyana can be invited to live with you when you find Orcin Camp, speak with the leader, and be invited to breed. (You don't need to breed)
You have to interact with 8 different Orcs as well.
is the option only there when you are first invited to breed? i didn't have a free room in the house yet when i got the offer but now that i do i can't find any mention of Elyana anywhere