Too big for 13.1 pony?

[Usain Colt]

My sister rides a 13.1 Welsh, I am wondering if she will outgrow her?
We just do hacking, no shows or competitive riding.
Because my sister is still growing like a mushroom I guess I'll use how big I am as an estimate. I'm 5ft7 and 60kg/9 stone, so if she grew as big as me, would she be still okay to ride her pony?
I don't have a good photo of the pony, but this is pretty much the exact same build as her, her estimated weight is 400 kg

 

[carthorse]

I can't see that height and weight being a problem since she looks a chunky sort, maybe too chunky looking at that photo and if that's a realistic estimate of her weight. Slim her down to a healthier weight, the slimmer and fitter she is the better she'll be able to carry a rider.

Just realised the photo isn't your mare, but if she's in a similar condition what I said still applies. On that pony there's too much crest, no clear neck shoulder divide, the belly is below the elbow, and even in a photo I can see fat ripples on the quarters.

 

[Jessey]

9st is unlikely to be an issue for a solid native, her legs might get a little long but often natives take up long legs well.