If your daughter is scared of creepy things like HM that are supposed to be 'funny scary', then you probably shouldn't even consider Forbidden Journey, UNLESS she's ok with closing her eyes and listening to things. If that's the case *SPOILER ALERT* Tell her to start closing her eyes during the quidditch pitch scene once Harry shouts out 'Dementors!' and have her open them again once Harry says 'Let's Get out of here!'
The spiders are a bit creepy too, and spray you with water. The whomping willow is a cool effect, but could be creepy too.
The dragon isn't creepy to me at all.
As for Escape from Gringott's, there's a scene with trolls who are stupid and therefore more laughable than creepy. But Bellatrix (a character from the later stories) does show up and scream some curses at you, and as someone mentioned earlier, she may want to close her eyes for a bit when she sees the snake. Other than that, nothing too creepy, it's mostly actiony.
No matter what, remember that it's a vacation, so people should do what makes them happy. The theming in this area is the best I've ever seen (including Disney), so just strolling around with a butterbeer or ice cream is a blast. I was a huge chicken when it came to rides and now I'm a junkie, so I've been on both sides, and know how much it can ruin a day when someone pushes you on to a ride because they 'know you'll like it' and then it's as bad or worse than you expected.
ETA: *MORE SPOILER ALERT* On the Hogwarts express, the ride is different in either direction. One direction has a dementor that comes on the train and walks through the aisle. All you see is the silhouette, but again, could be creepy.