My[36M] girlfriend [40F] is super ****** that I checked on our female houseguest before bed.

I originally posted this in /amithe*******, but apparently it was a little too relationship-y for that sub so I'm seeking advice here. I'm also seeking validation that I'm not in the wrong here.
So the other night my GF had a friend stay over. We met at the bar after I got off work, everything is super cool, we hang out at the bar for a while cracking jokes and ****ing around on the jukebox and drinking, and later retire to our place for more drinking and games and general good times were had by all.
So things start to wind down, and everybody starts heading to bed. Friend retires to my bedroom, while GF and I get ready to hit the sack in her bedroom. We have separate bedrooms but will often sleep together in her room, so it just made sense to have the guest sleep in my room. Before I crawled in bed, I knocked on my bedroom door, waited for friend to say "come in", and went to make sure she was all good before bed. I turned off my computer, asked her if she needed anything, she said no I'm good, I wished her sweet dreams and went back to go to bed with GF.
Now she's all mad at me, and telling me that what I did was super inappropriate, since the guest is a woman and I am a man. I think that this is just common courtesy when hosting someone in your home, regardless of gender. Of course there was no weirdness or creepiness associated with our interaction, and we had been hanging out and enjoying each other's company all night, so I was not a stranger. AFAIK our guest didn't say anything about it, and thanked me in the morning for letting her crash in my room.
I am aware that women face unique challenges when interacting with men, and I try to be cognizant of that if I need to approach a woman in a vulnerable situation, or run into a female stranger unexpectedly. I absolutely acknowledge that there are many situations where a woman would be threatened by the presence of a man, but it seems to me that the circumstances surrounding this situation made it so that it really wasn't one of those situations. We had also been hanging out for hours and having fun with the GF, and I felt perfectly comfortable approaching her, we were 100% on what you would call friendly terms and I did not feel like I would be perceived as threatening.
Dating.mobi, please tell me if I am way off base here!
Note: GF had already given her a glass of water and an aspirin before I went to check on her. I was unaware of this.
Additional note: I also should clarify that she says since we had just met that day it was inappropriate. They have been friends for years.
TL;DR: I checked on my GFs friend before going to bed, the GF is saying it was super inappropriate, while I view it as just common courtesy when hosting a houseguest.


Source.