Nice.
I like Gabrielle's parents' reaction, which seems to be a reasonable balance between natural concern and acceptance of their daughter's needs. I know how tempting it is to simply say "the parents of a Veela are different," but it does add a certain realism to the story.
I'm a little weary of the "Harry must become tall" thing, but I'm glad you didn't have him end up at two metres--six foot six or seven is just plain taller than anyone needs to be, and IMHO is one of those things, like superpowers, that makes a story become too annoying to read, whereas six foot is an ordinary tall person's height.
Personally I hope to see it become Harry/Gabrielle/Hermione, but as you please. I'm glad to see that Hermione and her parents are being thoughtful and wary of Dumbledore. And what you've done with the "Great man, Dumbledore" line is clever--I'm looking forward to seeing what comes of it.
You have got a fair number of minor errors--missing commas, typos, and suchlike--but it's still very readable.