I used to have a lot of fun flying on rollercoasters when I was younger. Tower of Terror is all seatbelts now, so it shouldn't be a big worry. Rockin' Roller Coaster has over the shoulder harnesses, so as she shouldn't be able to fall out. Splash Mountain doesn't have seatbelts, but as long as she doesn't try to leave the log (boat) and stays seated she should be safe. The only roller coaster I'd be much concerned with is Big Thunder Mountain. Most of the time I've ridden in my own seat (no one next to me), or with a family member. This last time I rode, I was boarding the train and found out that I had someone ridding with me. He needed the shared lap bar to be higher than it should be for me to feel safe. I didn't fall out, but didn't fell as safe with the lap bar that high. I would recommend that if she rides, she rides with a friend or family member that can watch and make sure she won't get bounced out. I don't think it's likely, but I didn't like thinking I was by myself and then finding out I was riding with someone who needed the bar higher. Many rides are designed for adults far larger than me, and I can normally ride without holding on and still feel safe. I think part of it was that I'm only used to having a bit of room to fly off the seat on a ride, and the extra room was not necessarily dangerous, but surprising that I didn't bump the bar when I thought I should.
