As long as she doesn't panic at the site of dementors, dorky spiders, etc. She'll be fine.
If you are asking the more delicate question about whether she'll be safe from pervs, I'd say yes, once they're locked into the harness, the range of motion is pretty limited, but if worried, strike up a conversation with people in line with kids and see if there is a group of three she can tag along with.
And, it's not uncommon if you are there during slower load times, like early am, or evening, that she might be on the ride vehicle by herself.