I wish this were a joke.

Backstory, I'm an American volunteer in a developing country and every volunteers lives in village. As such, I have a latrine about ten feet away from my house. At night, it's too dark. Been here for a year now, I've trained my body to not go to the bathroom but I leave a bucket for guests.
Another volunteer, let's call her MJ, asked if she could stay over this week. MJ, while nice, isn't considerate of others.
A repeating issue with her is her memory loss. MJ is only 29 but she forgets things easily. We take malaria prophalxis pills every day, she's always forgotten them every time she visits me or travels for work trainings. Me and others have had to give her some pills. She's forgotten her bags in the back of buses. She's misplaced things, it can be directly in front of her, and instead of looking, she'll ask you where it is.
Fast forward to this week, she stays over one night. I give her the bucket. Told her that I throw it outside after use. I don't let it sit overnight unless I'm already in bed. She doesn't do that, even though she goes to bed at 10 pm and I was in the living room till midnight. Can't force people. Anyway, I come to bed and she pees again, covering it with a lid. The next morning--I've told her before that opening the lid will cause it to stink since it's been sitting there for 8-10 hours--she can't hold it for the 30 second walk to the bathroom so she pees. This shows how little she cares, she wakes up early and does this, leaving me, who intends on sleeping a while longer, with a pee smelling room.
I'm not watching her pee but I hear the bucket move so I assume she took it out and dumped it, cleaning it. We go about our day, she leaves my village and I go to work. I come back at 1 am the next day, sleeping in. All day, I smell something weird but assumed it was my dirty laundry. Around 5 pm that day, I decide to check the bucket and lo and behold, her pee is there and it smells rancid.
I was beyond disgusted. I threw it out and the smell made me gag, I couldn't eat my dinner. I texted MJ a picture of the bucket, saying that she's not welcome in my house and she can't contact me anymore about non work related things. I said this was inconsiderate even if this was an accident, she is 30 years old and I shouldn't have to clean her pee. She did apologize, saying she didn't mean to and she'll keep her distance.
I don't think I was being unreasonable. There's being forgetful and then there's being inconsiderate. In the same few hours she'd been here, she'd spilled my skincare which I'd gotten from the US and is hard to replace, she didn't apologize. I cleaned it up. She'd also forgotten our groceries in the car and misplaced her padlock. What do you guys think?

I understand your frustration and feeling of being disrespected by MJ's actions. It sounds like her forgetfulness is impacting not only her own life but also the lives of those around her. It's important for her to take responsibility for her actions and make an effort to be more considerate of others. It's completely reasonable for you to set boundaries and prioritize your own well-being in this situation. Hopefully, MJ will learn from this experience and strive to be more mindful in the future.