Are you buying, or is she yours already? From that picture I would say she will grow - she looks like her front end really needs to catch up. Not more than a couple of inches though. What do you need her to be?
I bought a 3 year old who was 14.2 at the withers and 15h at the top of her croup who was "certain" to grow. She is now 16 and..........14.2 at the withers and 15h at the bum. They don't always grow, even when they are bum high you know.
It doesn't really matter how big she is if you feel right and comfortable on her, and especially if she rides bigger. I bought mine as a 5-nearly-6-yo last year. He was 14.3hh, quite bum high and nothing on the front end. He's a native type (I say type because I thought he was a connie x but now thinking he's a NF x cob! long story...!). At the end of this summer I measured him at just a shade under 15.1hh and he's really bulked up, but he won't go up anymore now (he's 7). He did grow and I'd have liked 15.2hh as well, but it isn't happening. However, he rides like 16hh so he doesn't feel like a big pony/little horse, he feels and rides much bigger.
I like the mare in the pic and agree with Wagtail, you can always sell her.
Just to add, I also bought a 5 year old 16h WB because he was a "tidy" size (not into giant horses these days). Well, now he is 8/rising 9 and over 17h. Horses! They never do what you expect them to, do they?
Just to add, I also bought a 5 year old 16h WB because he was a "tidy" size (not into giant horses these days). Well, now he is 8/rising 9 and over 17h. Horses! They never do what you expect them to, do they?