I'm going to be rude at my roomate for spending two hours in the bathroom
Why are you mad she was in the bathroom
She's just disrespecting her housemates by pooping for so long.
Maybe she is not trying to be rude and is just unaware. Some people find it relaxing in the bathroom.
I don't care I'll scream at her the next time she's in there.
There better ways to deal with it, you don't need to scream at her for such a small thing. Talk to her and let her know that maybe she finds relaxing in the bathroom but it can be inconvenient for housemates.