Gaëlle is a really beautiful, elegant name. I have an interest in everything Celtic so I find this name appealing on all levels. Not just because of how elegant and sophisticated it sounds and looks, but also because of its connection to the Gaels. While as I said it feels very elegant and refined, imo it's a kind of rustic elegance, so in that sense I think I could see Gaëlle as a cottage core name. I think I have an easier time imagining it on a grown woman than a little girl as it has a rather mature feel to me, but it could be just because I don't know any Gaëlles personally.
I have a little cousin name Gaelle. It's a pretty name. It's very unique. We pronounce it (Guy-el). Don't say it too fast or too slow and it will sound nice on your tongue.