She's a nice mare for a mustang, but I feel the need to ask....why are you planning to breed her when there are thousands just like her (and better conformed) that you can pick up for $125.....color, size, temperament, and conformation of your choice?
Anyway, she's a decent mare but does have quite a few faults (like any mustang, lord knows mine has his issues LOL). She's very long through her back with a weak coupling, and it also appears she's got the start of a sway back, which being bred could make worse. She is slightly calf kneed, her right knee is a little offset and she's a bit clubby on her right front hoof. Any or all of those may be genetic and passed on to a foal, possibly ending up worse than what she's got.
She's a bit camped under on her hind end and post legged, straight through her hocks and stifles. Her shoulder and croup have nice angles but her neck is short and her head is coarse.
Have you browsed the BLM online adoption gallery? They've got dozens of horses to choose from, most of which are young but some are already gentled on the ground and there are a few started under saddle. https://www.blm.gov/adoptahorse/onlinegallery.php