Nice horse tho with that crest and her age I would have her checked for Cushing's disease. She looks sound at 24 and still rideable. If she is sound and still rideable, it would be better to NOT retire her.
She does appear to have a hatchet neck (dip in front of her withers).
She looks great for 24! I have seen a lot of standardbreds that seem to be hard to keep weight on, but she looks great! I would worry a bit about the cresty neck, maybe look into cushings like someone above suggested? Otherwise if she is happy and pasture sound (you mentioned she was retired) she looks great! Nice strong hindquarters, a bit of a hatchet neck, but nothing scary!
Thanks for the responses everyone :) She's retired due to being a bit arthritic and her hips give her a bit of trouble, but otherwise she thinks she's still a filly ;) We used to do just pleasure riding around the yard, but she also did some dressage in her younger days.
Thanks for the mention of the cresty neck, I didn't realise it was an issue, so I'll look into it!