Any idea of her breeding (other than Heinz 57?) What do you know about the dam? How big is the filly now, and how old is she?
She seems to have shorter legs; youngsters are obviously their “leggiest” when they are under a year old (since the legs are close to their adult length at a relatively early age.) I have had two other babies, both TBs - one I bred (sporthorse TB lines) and the other I bought as a weanling, so I was able to assess them at various growth stages. One of them (the smaller of the two) had a shorter neck and back as a foal and then lengthened out as a weanling - it was more noticeable because he had been a pretty compact baby; he wound up with a good moderate length of neck and back, and from yearling to adult he looked pretty much exactly the same - he finished at 15’2", another example of horses who will end up small tending to look more like their adult selves through growth phases, and less “gawky and gangly.” (Sire was long backed and long necked, dam was medium.) The other one had a long neck and a long back as a baby and that didn’t change; much like my Ella. He was leggier, and wound up 16’2-16’3" - he dd go through the typical weanling fuglies but his “basic structure” remained the same throughout his life.
I have boarded at a breeding barn for 9 1/2 years - this has been very educational because I get to see foals become weanlings, then yearlings, then 2 and 3 year olds. Most of them are TBs destined for the track (but some are WBs), and they go through many body changes, but the “bony landmarks” tend to remain consistent even when they go through fugly stages. (I have seen about 150 or so in the years I’ve been there, so a lot of first-hand examples of growth stages as they grow up in front of me.)
The young TBs don’t have as much “bone” (in general) than my WBs - but as mentioned above, it’s more the density than the circumference in many cases. In the winter, ALL baby legs look thicker because of all the hair!
, it can be deceptive! ALL hooves look *tinier" than usual - and of course feet grow bigger and wider as babies grow.
What is your eventual goal for a young horse?