She is a very cute horse. I see no stifle stiffness, but her way of going is a bit like a deer, "pronking". I see that a lot in Arabs. But, again, it could be that she is being chased , so is moving defensively.
She is downhill, for sure, so you might not like that. How old was she? She may still have some growing to do. Look at her sire/dam for a good idea of the adult conformation.
She has really good balance and knows exactly where her feet are. Did many perfect flying lead changes. She seems really level headed. Several times she asked "can I come in now?" not really scared.
I think she'd make an excellent trail , all aroud horse.