This didn't sound right to me, as Robin has always been taken away in all of my games, usually sometime in October. So I went and tested it by repeatedly pressing the "go forward 24 hours" cheat without having done anything except having been introduced to her, and it was October 30th that Robin disappeared from her room (which seems actually a couple of weeks later than she usually is when I spend a decent amount of time trying to help her out, but whatever).
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So even avoiding her doesn't prevent it.
Azi VonVeil Yes.