When are you supposed to sit down?

So here when the boss walks in you're supposed to stand up as a sign of respect.

Except my boss walks in and out so fast that by the time I'm ready to stand she's already left again! And then sometimes I do manage to stand up but then I don't know when to sit down and I just stay standing there like an idiot. Today I was standing for like 10 minutes while she was talking to someone else in dari. I started to edge towards my seat again and then she turned around so I froze. But then she just continued talking. It was a constant game of cat and mouse...that I don't think anybody else was playing.

Another time I stood when she walked in the door and sat down as soon as she started talking to someone else. A minute later she came to my desk and I nearly fell out of my chair trying to get up again.

When are you supposed to sit down?!