When I first rode Gringott's, I was more scared of the first drop due to the angle and how we hung for a moment, the actual drop is nothing (I think they mainly do that for intimidation purposes). As it's a drop that is short in comparison to other drops and also moves towards the side as it happens as well. So, it does not feel that dramatic of a drop either. It's very quick. Most of the ride is interaction via screen of the chracters, there are only two real rollercoaster bits in general and are extremely quick and completely pitch black.
She should be good to go. This is coming from, yes, someone who does not like drops (however I do often just deal, as I often ride JP).
Bluto, once again, more so makes you scared and intimidated due to the anticipation more than anything (like the beginning of Gringott's), as it just seems to climb, climb, climb, but the drop itself isn't that bad, however you will get soaked afterwards and the speed of the rafts do quicken afterwards, as someone previously said. Other than that, it might worry her as it seems to go higher and higher, but the drop itself isn't nothing. It seems intimidating, but the drop itself is not something that makes your heart drop at all. At least not me. So, she'll more than likely be scared of the unknown and anticipation rather than the actual drop itself. At least that was my first experience riding it. Now it's a breeze, just like Gringott's.