I suspect the outcome in these cases also depends on the particular drug involved. If my daughter were to get a prescription for 600 ibuprophen to get her through the track season and I take a few instead of taking three Advil, I don’t see any harm. Xanax, Oxy and others would be a different story.
Personally, I don’t actually believe the claim that she didn’t know it was inappropriate to not share Xanax unless she also had her own prescription and only took them out of his bottle a few times. I also have a serious issue with any clearance holder self medicating with something like Xanax.