I think you should ask him if he'd mind if you invited her out for coffee, just you and her! After all, if you're going to be such important people in each other's lives... "co-primary" or "sister wives", potentially... then shouldn't you two really know each other? You're not going too far by wanting to fully consider her needs, not at all. Ideally, the two of you can be friends and allies. And at the very least, at this stage of things where living arrangements are coming into play, you should be more than passing acquaintances.
Me, 30ish bi female, been doing solo poly for roughly 5 years. Gia, Clay, and Pike, my partners. Davis, ex/friend/"it's complicated." Eric, Gia's husband. Bee, Gia and Eric's toddler.