Thanks for the suggestions and advice everyone.
I think we have most of the details ironed out, it's making her feel welcome, comfortable, and valued that I'm most concerned about. I don't want her to feel like she has to hole up in her bedroom all the time. We want to do whatever we can to make her feel welcome and appreciated, but at the same time give her her own privacy, etc.
She will have a double-bed, with her own linens and towels. I think hanging some family pictures is a great idea and thought I might put a mirror in there as well to open the room up a little more. The bathroom has its own lock from the outside. She'll have a recliner in there, a small writing table, and her own TV, so I'm not worried about her taking over our areas, though she is welcome to join us. As evidenced by my screen name, we both share a common interest in Downton Abbey, so having her come out of her room to watch it with us is fine and she's welcome to sit with us whenever she wants. If she wants something different she'll go into her own room.
The cooking I'm not worried much about either. DD and DH get breakfast together, then DH takes her to school. My Mom will get up and do her own thing. She's welcome to join us for dinner. She'll buy her own food, but she's welcome to take ours too. She eats out a lot (by choice) and I don't expect that to change really. I definitely don't want her having a toaster oven or food in her room because of the potential for mess and pest problems. A mini-fridge would be one thing, but we don't take food all over the house. She knows all of that and hasn't asked for anything other than a shelf in the pantry and a shelf in the fridge--which we easily have.
The biggest issue we've had is visitation from her brothers, my Uncles, who live out of town. One, because he is so nasty to DD, is not welcome to stay in our home. He will have to stay with my Uncle who lives in town. He can visit Mom at the house, but he cannot stay there. And the other, who is widowed but has a girlfriend, is welcome to stay at our home, but not in the same bedroom as his girlfriend. Mom didn't like them doing that at her house either, but didn't figure she could say anything. We've made it clear that this is a non-negotiable policy in our home. She has agreed to abide by this and we will take care of handling this with my Uncle should the need arise. That was by far our biggest issue.
Now the rest is just making her feel welcome, wanted, and appreciated.