Maybe we didn't actually fight Glint herself there. Maybe we only met a smaller 'copy' of Glint. If she's powerful, she might be able to create duplicates of herself for her protection, which would be smaller, weaker, but still powerful enough to create an illusion of the real thing.
If I were a dragon, and had a group of heroes coming to see me, I wouldn't need to be able to see the future to tell that they may decide to kill me. Humans are a very violent species, and have been humting dragons for years, just because I'm going to help them, doesn't mean one of them won't try something. So if I could create duplicates of myself, I'd create one to talk to the heroes, and if they attack the duplicate, at least I'm alive, if not, well, I get someone to talk to for however long the duplicate lasts before the magic that created him wears off.
Of course, that's just what I would do, and there is no evidence that Glint can create duplicates like that.