She acted like I was about to chew her head off 😕

My new co-assistant Amber, who started this week, came back today after being gone yesterday afternoon for an appointment she forgot to tell me about, though she told the two leading managers (who didn't tell me because they assumed Amber would, lol). I just told her today to next time please be sure to inform me of that since I am her direct supervisor and need to know the most. I did so very cool and collected, not trying to make it seem like I'm chewing her out or anything, but her reaction made it seem like I was. She got all quiet was hanging her head a bit... I had said on Amber's first day earlier this week that she reminds me of myself when I first started and I suppose I would take even slightest criticisms pretty hard. I guess now I know how that looks from outside perspective. 😟