If she knows that you dress and has accepted that but doesn't want to see it, she should be willing to warn you when she is coming home, either by telling you a time or calling early enough for you to change. It is she who doesn't want to see it, not you who doesn't want her to see it.
An option (a bit sneaky and you wouldn't want her to find out about it) is to use a tracking service on her phone or a GPS tracker on her vehicle.
