My living situation is as follows: I live in a two-story house with my mother and no one else. Our Bedrooms are upstairs, together with a small bathroom without a toilet. The toilet is downstairs. We live in the middle class of a first world country. I'm a 16-year-old girl.
My mom has to use the bathroom almost every night, but she is, in her own words "too lazy to go downstairs". So she goes to the upstairs bathroom, empties the bowl with our showering supplies and reliefs herself in it. When I get up in the morning to take a shower she is still sleeping and the entire place will smell of the bowl. It is a four square meter bathroom so the bowl is always forced up into my personal space.
She sometimes forgets to remove it, so when I come home from school and go to the bathroom to eg. wash my hands, the bowl will stand there in all of its at this point 12-hour old glory. When she cleans it, she just empties the bowl, rinses some water through it and puts our showering supplies back in.
I told her (not very compassionately) that I find it disgusting and unhygienic and that we need to find another way to solve this. She said that, as mentioned, she's too lazy to go downstairs and I shouldn't be such a squeamish baby and just bring it down and pour it away myself.
Eventually, she bought a bowl with a lid, but guess what - She says she's too lazy to put the lid on cause she just wants to go to bed again after she relieved herself.
How can I get her to use the bathroom? Or how do I not have to share a bathroom with a bowl of loo? This probably includes the consecutive question "How do I convince a person to do something if they deem everything inconvenient and inconvenience as enough reason to not change? eg. I can't convince her to use the bathtub and rinse it away cause it's not so convenient.
I'm in Germany, and the cultural context is just the German one (no religion, no immigration background). It is definitely unacceptable in our culture. This is not a joke/trolling question and while I have an account on Stack Exchange I don't want this question to be related to my account.