I have a 15yo who could carry off Pixie, although she wouldn't, because of Pixie Lott. She is petite, and dresses in a very distinctive, edgy, but mostly feminine style.
My 13yo could not. She is more sturdily built, and tends to go for a more masculine silhouette.
So, I would avoid Pixie, because you couldn't know whether the child could carry off the name, as they got older.
I have a friend who always calls one of her (15yo) DC Dolly. The girl's name is something else entirely, not even similar to Dolly, and a fairly classic girls' name.
You could use Pixie as a nickname, when she is small, and reassess as she gets older.
I really dislike Ottie. It doesn't even sound pretty to my ears. And certainly not a name an adult would wear.
I know you say this thread is strengthening your resolve to call your DD one of these names. But, really, it's not about you, is it? Your baby will be a whole person in her own right.