You know, you seem keen to have people give you feedback on your horses, and that's wonderful... It would really help if you put a bit of effort into standing them up correctly for us to do so.
Not one of the still shots does this filly any justice at all.
That said, in the videos, the fact she is post legged and very downhill doesn't change. That she is just over a year gives her balance some leeway, but as mentioned, she will stay too straight behind. The reason we might say this would hamper her is that it can really reduce the thrusting and turning power of the hindquarter - and both are important in a barrel racer.
Now, it is true that some great racehorses have been both downhill and post legged... But barrel racing has the added challenge of tight turns. She is currently very very straight behind. I love that you seem to seek your vet's advice, but remember, a vet is not necessarily a conformation expert, nor are many of them competitive riders... So conformation feedback from a vet is not always going to give you the same results as that of a professional judge, or a review done by professionals of the sport in your area.
As for the rest of her, I will say that the yearling year is often the most awkward for a young horse... Wait until next year, or her third year to assess her, it takes 8 years for ANY horse to be "mature" so she has a lot of growing and changing to do still. Some things won't change about her, but it is currently a little unfair to try to predict her future based on this stage of growth.
If you really want to get some feedback on her that you can stand on, enter her in some halter classes, even at a local level. Listen to what the judges say. if there aren't many halter classes available to you, you can always approach local breeders and ask their opinion (do a proper set up, have an extra hand if need be) - many are willing to be honest and fair to a young person wanting to learn.