I have read Harry Potter but it's been a while and I have to admit that I don't remember Lavender too well in her own canon. From what I remember, she was a secondary character we didn't see a tremendous amount of--although we certainly did see enough of her to leave some kind of workable impression.
The way Harry Potter is written works well for a novel but leaves us with dozens of characters who are drawn with too few strokes to feel complete in an rp sense. So it's awesome to see a character who was drawn in broad strokes come to life with strokes that are both greater in number and more specific.
Lavender does at times feel inconsistent. This may be the byproduct of not having hit your stride quite yet, or it may come from Lavender's available canon being somewhat limited. It may also be a conscious choice to showcase how being turned into a werewolf is affecting her. Whatever the case, inconsistency is usually fairly easily solved just by doing more with a character and building reliable ties.
I'm excited to see more of Lavender in Marrowood, especially since you're taking such an interesting and unconventional direction by making her a werewolf.