If I were you, I would book a hotel room nearby or somewhere in the city center for her.
Hotels in Thailand are not that expensive. (choose whatever suits your budget, or hers)
After breakfast, you and your husband can go to pick her up for a sightseeing.
Late evening after dinner, you can bring her back to the room.
You can also pick her up to visit your house for a dinner for an hour or two.
Leave your husband and her sometime (off) for afternoon coffee or so.
Just my personal thinking. I think it's kind of akward for me to be together almost 24 hours a day.
I'm just a person who need some privacy.

I guess her daughter/son is not a young kidany more, and doesn't live with you and your husband.

Good luck!