Did she mention any reasons why she'd like you to leave, or was it more of just a 'this is taking longer than expected' sort of thing? That sort of conversation is never easy, but if you've got a chance to understand and learn from it, it can at least be sort of useful in a weird way.

I'm glad the teachers at the school are feeling comfortable with sending you students, because that does show trust; while warning would be nice, don't be afraid to be proactive perhaps and offer help at dedicated times, so that they get the hint that a little bit of scheduling might be useful?