That horse doesn't look comfortable at all. She's swishing her tail a majority of the time, since she doesn't run barrels regularly that probably means she's hurting somewhere. She also changes leads really awkwardly twice, like she's uncomfortable in her strides.. If your friend rides her a good bit I would suggest having her vet checked and probably a chiro out too. It could be anything pain related, from ill fitting tack to rider error causing soreness.
Usually with the halter bred horses, they are bred to be bigger horses and have tiny feet. Those little feet can't hold up to a lot of stress when carrying that big body and do serious damage to their legs if overly stressed..like running barrels.