For me, it would depend on the child and how they were really acting and the child themselves. For instance, my daughter would tell me that she was scared of any of the rides with height restrictions. If she was just hesitant about the ride, I would talk her into at least trying it (and I'm not above bribery...promising an A&E balloon goes a long way for her). However, for some rides she just got herself into a panic. I remember this about RNR....she kept saying all through the line that she wanted to ride and then we got to where we were actually loading and she started freaking out screaming and crying and saying that she was too scared. At that point, I sent her out the exit (dad was waiting with her too short sister there, and my other child was already strapped into the ride).
I would also try to find out exactly what it is that she doesn't like about the ride or what could make her feel more secure when on the ride and then try to solve that problem. For instance, maybe she had an issue on BTMRR because she was riding with you so the restraint didn't feel secure enough for her. If you want her to try 7DMT, you could explain that the restraint is individual and she can make it as tight as she wants. You could also explain that even though the roller coasters feel like they are going very fast, that 7DMT is actually SLOWER than the speed you drive on the highway. I would also let her have a choice of who she wants to sit with on the rides.
Another idea, kind of similar to bribery, would be a quest for riding rides with a reward at the end. The reward could be something that you would plan anyway or an extra treat for the family....just something to get her to try something new. For instance, you could give her a quest in MK to ride Splash, BTMRR, and 7DMT. If she rides all of those you could promise a dinner at BOG or CRT or a makeover at BBB. It wouldn't have to be something that big...she could get a pin or a balloon or something you might already plan to buy her on the trip like a t-shirt or Mickey Bar. If you can still get the paper Disney dollars, you could give her $2 for each ride towards souvenirs of her choice....like a quest to earn spending money.