How do I ask my boss to be a little less... Disgusting?

Okay, crappy question I know, but entirely valid I promise.

So I started working in an office space about 3-4 months ago. Everything is great. My boss is a wonderful older asian lady who is one of the kindest people I've ever met. But I have a small issue. 

In this office there are 3 of us in total. Me, my boss and my other boss. My other (male) boss works out in the warehouse (ish) area all day long and has his own bathroom. My female boss and I share a toilet. 

Every time my boss goes to the bathroom, she seems to pee on the seat and not notice. So every time I go pee, I have to wipe her pee of the toilet seat. There have even been some days where she has left the toilet full... While on her period. 

Seeing as she's my boss and she's so kind I'm not sure how to approach this subject. I don't like being straightforward with her as this can sometimes lead to a communication issue and then other issues ensue.

Does anyone have any advice on how to approach this?