That's reassuring, thank you all. She is 15months and just over 21lbs I think. Apart from the early weeks she has never gained more than a pound every 6weeks so I'm finally starting to realise that it will take her a while to gain enough to put her into a large. It seems a bit weird though when I can gain 2lbs without even thinking about it, and it will take her months to do the same!
I checked, and it's actually the second to last popper so she's not quite as weeble like as I thought