She looks good overall, so I wouldn't worry. I would be MORE concerned about a youngster growing
too quickly... a pet peeve of mine. Too much weight on their joints, etc etc etc. Mine don't look like sale prepped yearlings (who sometimes look like fat 3YOs,) but I know they're strong and sound. (Obviously this doesn't mean starving them or stunting their growth, but it's apparent by the picture that's not the case.)
To address your question more specifically, each year I enjoy watching the yearlings change and grow, each at their own different pace. The runt usually ends up taller than the others at some point, and one day you look at the one who you thought would be small and realize he's huge... they all just have growth spurts at different times, so that makes them look smaller/taller than the others depending on where they all are on their personal growth curves. We have 6 yearlings out here right now, and they are constantly changing height order based on who has had the latest growth spurt.
My advice is just make sure the yearling has the appropriate amount of feed (not too much, not too little,) then sit back and watch her grow and change at her own pace. I'll bet she'll surprise you.