Does she have access to a run? And what bedding, are you using?
The reason I ask is because horses tend to pee where they won't get splashed. That's why they spread out so much to pee - they don't want to get it on their legs. It can actually cause skin issues of they get it on themselves too much on a regular basis.
I learned this tip from a waste management specialist, whose job is to educate others about properly dealing with livestock waste. She spoke to our horse club about composting and other forms of waste management, including how to take care of waste from your stalls.
Horses not wanting to pee on themselves lends to a nifty way to train your horses not to potty in the stall - remove all bedding. If the bottom of the stall is rubber, then the horses will get splashed when they pee. Eventually, they'll start going in their run to do their business, keeping your stall cleaner. Plus, the rubber is easy to sweep/scrape/spray off, making for quick cleanups. A friend of mine keeps all four horses in stalls with rubber mats only - and the mats are almost always clean because the horses just don't mess them up!