Posting for a friend (I have a dog and don't have such problems).

My friend has a cat, almost 1 year old. She has been taking it out on a leash and collar, letting it wander around their apartment complex. It's really quite cute.

She does this once a day, usually in the evening, but now the kitteh ALWAYS wants to go out with her, like when she's leaving for work and has no time to play around.

She's complained about this enough that I'm bringing it to you guys (after days spent trying to convince her to join POTD herself). So how do you let a cat know when it's time to go out, and when it's not? The cat looks so sad, meowing, wanting to go out with her. How do you train it?