I would try not to worry they all do it in their own time, and 2 and half isn't really to old to be in nappys.
All mine have been different.
With Ethan I tried to potty train him at the "right" age according to other people, it was the summer so we just didn't put a nappy on him, I was (it seems) alway cleaning pee of the floor I can't remember how long it took but by the time he was sorted I don't think there was a patch of floor that he hadn't pee'd on (lucky we moved not long after
)
Callum was 3, we tried him in the august before his 3rd birthday (which is october) but he really wasn't ready and after a couple of days was back in a nappy, and thats how it stayed until after new year when he said "mummy I want to wear big boy pants like Ethan" I told him if he wore them he had to go to the toilet. We only ever had 2 accidents after that.
Lily's only 18months we brought he a potty a few months ago, as she'd started taking he nappy off (when wearing skirts) when she'd wee'd in it or started holding her nappy, we aren't potty training but we have it there for her to get the idea when she's ready, she sometimes goes and sits on it when she likes also when we change he nappy i ask if she'll sit on her potty.
All children are different, I'm sure when she's completely comfortable with the change she'll do it with no trouble at all.
xSuzx