I appears that her rectum is recessed farther in than her vulva. This can be caused by age, being thin, being low-backed, having several foals, and other reasons. It also appears that she has been sutured in the past. Most race mares are sutured on the track.
EVERY horse that has a rectum that is recessed and a vulva the 'tilts' inward at the top of it SHOULD be sutured.
Suturing a mare like this without doing a uterine culture while she is in heat, only closes a uterine infection up in the mare. At the very least (if you elect to not go through the expense of a culture), the Vet should infuse the mare's uterus with a good broad spectrum antibiotic that specifically targets E-Coli and other Gram Negative Rods BEFORE suturing her.
We use Furacin Solution mixed with 250cc of Saline to infuse mares that are not going to be used for breeding later on. We always culture every mare that is going to be bred later on.
She should be a lot more comfortable after suturing her and if she has weight issue, suturing should help that, too. The discharge should clean up immediately if she is infused before suturing. The fecal contamination should also stop immediately.