Hi Katherine!
It's so wonderful that you visited us again at the Disney Parks Moms Panel! Your question touched my heart. I had this same question regarding my son when he was younger, before he received his wheelchair; he also has extremely low tone and cannot sit unassisted. In my opinion, you've chosen the best place to vacation on the planet because Walt Disney World Resort goes out of the way to make sure every individual, no matter what their abilities are, has a magical time.
You may absolutely bring your daughter's stroller into the restaurants so she can sit comfortably in it during meals. When we booked
Advanced Dining Reservations, we would try to include this in our reservations. With that being said, if you don't have it marked down on your reservation, just let the host or hostess know when you arrive at the restaurant to check in. They will likely remove a chair so your daughter has enough room to sit in her stroller at the table!
Katherine, I want to mention one more thing that really helped me with my son when he was in a stroller. If you stop at Guest Relations at any theme park, you can ask for a
Stroller as Wheelchair tag to attach to your stroller that alerts Cast Members to treat your stroller as a wheelchair. This comes in handy because if your daughter is getting tired during the day, she will be allowed to stay in her stroller throughout the majority of the queues and transfer from it (like a person in a wheelchair would) onto rides. We used this for my son and it was a lifesaver for him and me!
I'm wishing you and your daughter a magical vacation while visiting Walt Disney World Resort! Please visit us again with any future questions!
Beth