2'9", definitely: a) Best to keep moving forward; b) She's a horse! (I know the dilemma: we used to have a tiny little 14.2 thing with high whithers... wouldn't have dared trying to pass her off as 13.3, which is really what she should have been!)
She is just a horse - and at this particular club's shows if you're 14.3 and the rider is under 16 you can decide which way to go. Previously, dd has declared her as a pony - which has barred her from the more "serious" jumping but has allowed her to do things like the "Pairs" and Horse and Groom". I think she'll go 2'9 and reconcile herself to rosette-less-ness!
She's always loved doing riding club pony though because it gives her the chance to show off the nag - she's very good at that to sort of thing and dd loves the chance to keep her steady and collected and sensible while all around her all the little Thellwell look alikes are going bonkers!