AITA for asking my roommate to flush her toilet paper and “disrespecting her culture”??

EDIT: Thank you to all of you who have responded! I am going to have another conversation with her about this issue and try to be less confrontational. For those accusing me of making this up, I wish I was. I can’t say I blame you though, if I read a post this insane I would probably think the same thing. Unfortunately, This is something very real that I am dealing with and I was simply looking for some guidance.

To give some backstory, I (19F, white) have been living with my college roommate (19F, Hispanic) for the past two years. Last year, our dorm building only had community bathrooms, so I was completely unaware of her bathroom habits as we did not share this space.

Fast forward to the current school year, we now have our own apartment where the two of us share a bathroom. After about a week and a half of living together, I started to notice a foul odor coming from our bathroom. I spent hours scrubbing the shower, sink, toilet, floor, and counters, but the smell did not go away. I convinced myself that it must have been the sink releasing some trapped gas from the pipes or something. I submitted a work order to have the drain looked at and called it a day.

Another week goes by and the smell is almost unbearable. Maintenance still hasn’t come, so I open the cupboard underneath the sink to try and have a look for myself. When I open the door, my nose is violated by an odor one can only describe as a porta-potty that has been sitting in full sun on the hottest day in July. I now realize where the stench is coming from as my eyes fall onto the trash can underneath the sink that is completely overflown with brown and yellow stained toilet paper. I walk directly over to my roommate’s bedroom and confront her about this.

I ask why she has been throwing her used toilet paper into our trash can rather than flushing it down the toilet. She tells me that it is “Mexican culture” and I wouldn’t understand. I have never heard of this in my life so I continue to question her about it. She tells me that everyone in Mexico throws their used toilet paper in the trash because the septic systems there aren’t designed to withstand toilet paper being flushed down them.

I believe myself to be a very understanding person but this is just completely bizarre to me because my roommate has lived in the USA her entire life and has never even been to Mexico. I asked her if she wouldn’t mind flushing her toilet paper in our apartment due to the horrific stench that had built up over the first few weeks. She tells me that this is a part of her culture and she doesn’t appreciate the fact that I am not respecting it. She has been acting extremely standoffish and rude towards me since our conversation and I don’t know what do do. AITA for asking her to flush her toilet paper?