If she's already got an RX-8, she'll hate a Sequoia. The only advantage it has (and granted, it's a pretty big one) is hauling ability. Other than that, it'll be a pain in the ass to park, impossible to see out of, and thirsty - though from what I remember, the RX-8 isn't that great on gas either. That was my experience with the Suburban at least: I still can't park the thing easily half the time, the blind spots were enormous, and it guzzled gas. Not the greatest learner car. Before I got my 4runner, I preferred to drive my mom's old, falling apart minivan just because it was an easier vehicle to drive.
If you want to mover her to an SUV, I'd pick something a little smaller to start with.