Mine Train is without a doubt the smoothest of any of the coasters (big or small) at WDW, plus there is also a "break" in the middle of it so your daughter could take a breath if necessary...at which point she would also be quickly distracted by the dwarfs and jewels in the mine. It's not terribly long either, so it's no like she'd feel trapped on something if it turns out she's not a coaster fan. I have a soft spot in my heart for Goofy's Barnstormer, as it was my girls' first, but Mine Train didn't exist. Barnstormer can jerk you around, plus it's quite small, so not always a great combination for adults. To be fair, the imaginee...vil genius who designed the Mine Train vehicles didn't give much love to anyone with any height or girth whatsoever, but on the bright side, you definitely feel secure once you're wedged in there!