Roommate question: When I store my bike in my room, why do I need to put up with hers cluttering our small shared storage?

Okay, so she’s a bad roommate. Without going into all the details, a lot of it comes down to cleanliness and organizational issues. I don’t mind stuff being left out here and there, but for the most part, I like things to have a proper home that they can go to at the end of the day. I don’t care what her room looks like, but it’s insane messiness is pouring over into our shared space. Our living room is covered with her text books, clothes, shoes, etc. We’ve talked about this many times, and the only way to make it work is to have me constantly nag her.

My main question is, is it fair to ask her to do something else with her bike? Our rooms are about the same size, and I make room for my 10-speed in mine. She has her big beach cruiser in our storage room (which is the size of a laundry room and is off the kitchen with no door separation, so if it’s messy, you can see from the kitchen). I guess my issue is that if it’s our shared storage, and that’s what she wants to put in there, how can I ask her not to? I would say the rest of the stuff in there is half hers and half mine.

Any suggestions on the bike issue or dealing with annoyingly messy roommates would be helpful.