If she earns a good wage why doesn’t she rent a room in a shared house (with her friends) instead of moving in with you?
My concern would be that if you charge her nominal rent she’d never want to move out and pay higher rent elsewhere.
I do understand why your husband had to say yes to her moving in (how could he not?) and I guess he must have been quite stressed about it, which is why he didn’t tell you.
My experience of living with and ex and his 22 years old daughter was tricky. In hindsight, I should have done things differently, but at the time I was too emotional to think straight. My ex tried to make sure his daughter felt really welcome in his house, so the boundaries between daughter & partner were blurred. For e.g would take her food (or furniture) shopping and not even ask me if I wanted to go too (or instead). In the evening he’d sit downstairs with her in the kitchen instead of coming upstairs to the living room to watch tv with me (on nights when she didn’t want to watch tv). She’d go in our bedroom and take things from our en-suite bathroom but my ex would refuse to tell her off. Of course I didn’t care about the shampoo etc but about her going through my stuff. These things may seem insignificant but they made me feel jealous and caused me a lot of pain. Especially when my ex wasn’t warm towards me.
But I do feel bad that I wasn’t more mature and didn’t act differently as it must have been hard for her too to be in her father’s house with me there. And it was definitely stressful for my ex.
So, OP, if your SD moves in, I would set clear boundaries from the outside about how much rent she should pay, who does the cooking, cleaning etc. I would be inclined to say ask for a decent rent so she learns how to budget; and then you can give some of it back when she does move out. I would also set a max time for how long she should stay with you.
It might work out well, you never know. She may be out in the evenings with her friends and she may be nice to have around.
but gosh, I wouldn’t want to be in your shoes, I simply wouldn’t want anyone else in my house