Do you mean cute, petite Rosie currently at St Annendwarsstrat 1-4 on nights? -
https://www.ignatzmice.com/forums/viewtopic.php?f=16&t=23143.
If so then I'm not sure she always keeps to the same day off....
I visited in November and she'd taken Monday off that week.
I'd guess Monday is her most likely day off (it used to be Sunday at one point) but I don't think it's 100% fixed from week to week.