The Roommate Freak-Out of The Day

I've had a long day and little sleep to come home tonight to a roommate whining about being unable to sleep because the cat comes into her room. (By the way, I decided to take a nap in early evening only to be woken up by her cello playing so yeah.) I can understand if the cat is wailing and meowing that it would be disruptive but walking? I know she doesn't want the cat in her bedroom (reasonable), and I understand she needs her door open to enjoy the air conditioning (also perfectly normal), but what can I do? She wants me to constantly watch the cat, which I can't do. Cats are quiet so how am I to know what she is up to, and I'm not going to close my bedroom door to keep the cat in. I need AC too! Now, she thinks I should get a child proof fence so the cat can't go into her room, which is probably not a bad idea, but then, she shot down her own idea because she will have to take off the barrier every time she needs to get out of her room. Sigh. I can't wait to move to a place where a cat walking around is not a crime.