My roommate doesn't clean after herself?

I currently stayed in a four bedroom suite and share a bathroom with one of my roommates. Let’s called them roommate A,B, and C for the sake of argument. I share a bathroom with roommate C, the roommate that rarely talks to us and that we hardly see around. Unless I ask her to do so otherwise from time to time, she almost never cleans after herself. I live on campus before and I never really have problems like this with my last roommate i.e. where we both compromise and have a weekly bathroom routine. C and I didn’t really have a routine. We both agreed that we would clean up after ourselves and take turns supplying the toilet paper after it finishes. Lately, I seem to be the only one that is supplying my own toilet paper and tried to ask her if she has more available after I ran out a few weeks back (I still currently kept extra rolls in my room).

She also leaves her hair and other personal things all over the sink. She would also leave her dishes in the kitchen sink until me and the other roommate decided to put up a sign.

Before spring break I cleaned the bathroom up and everything else after myself right before I leave. Not too long ago when I return to my suite from spring break and went to use the bathroom, I lift up the toilet cover to discover that she didn’t flush! A grown woman who doesn’t flush after herself before she leaves. (Sadly this would be her second time, the first time I choose to ignore the problem and flush it anyways.) I have to step outside of my own suite to use a public restroom instead. Right now I’m expecting C to return back and flush after her own mess when she notices the stench.

I don’t want to make her feel bad for calling her out or by telling my other roommates about it. A and B on the other hand seem to have better bathroom compromise than C and I. I also don’t want her to get defensive either or resort to an argument if I tried to talk to her. The ironic part too is that she works with student housing and resident assistants, yet she doesn’t know how to take care of her habits on campus.

How should I deal with my roommate at this point?