What if she were living with her sister? That’s “family” isn’t it? - but no, that would not be coverable.
The lifestyle in this case is perverted, however there is something to be said for coverage because you still are PAYING for the partner.
This is why Vermont went to Civil Unions instead of "Marriage." Legally it's justified. As much as I think the life style is convoluted my intellectual honesty says Civil Unions are equitable.