White dicharge makes me think infection. Could have a uterine infection, esp if her whole "area" is saggy with age, or just has a sunken conformation. The poop can get into the vagina and stagnate in there, causing infections. Some horses get Caslicks (sp?) . The vagina will be stitched closed to stop urine and poop from getting in there. For broodmares, the stitches are cut and re-sewn for breeding and birth. After a chronic infection, mares can become sterile, and are sold as they aren't productive as broodmares anymore. A chronic infection can also make it hard for them to keep weight on, so I would see about it. Sometimes a vet can "flush" the uterus and prescribe anitbiotics, may need the stitches afterwards, and/or a hysterectomy of sorts.