I have pretty severe motion sickness. If it goes upside down, I can't ride it. If it spins, I can't ride it. If it's hot out, and I'm already tired, the carousel can make me urpy. I can ride BTMR, 7DMT and ToT just fine. I cannot ride Space Mountain, RnRC or Everest. I've never tried RnRC, but have ridden Space and EE.
I don't ride Everest anymore, but will wait in line (FP or Standby) with my wife, then just bail at the load platform and let her ride alone. The backwards part, including the nearly sideways double helix, turns my face white and covers me in sweat. I have to sit down for a while afterwards, and there could NEVER be a second ride. I think I've ridden twice, maybe 3 times. I regretted every one of them.
If she wants to say she tried it, get a FP for the end of the day, so if it makes her feel ill, it won't ruin the rest of the day.