Is OTHER wrong in the post ? POST : Sorry will be a bit long.

I have a friend I'll call C.  She started at my work a few years after me and knew noone in town.  I introduced her to 99% of her friends here, we are very close and have worked together for several years now.  Shortly after meeting her, I introduced her to another close friend of mine I will call D.  D is from the same country as C.  They become friends and hang out etc.

D and C fight on and off over the years.  D becomes very bad at keeping in contact with us.  When C got married last year, D pitched a shit fit because D expected her daughter to be a flowergirl and C said yes, but asked that D keep her daughters hair long until the wedding so it would be in keeping with the bridesmaids etc.  D also cracked it because C said while the kid could be flowergirl, no children were to come to the reception .  Plenty of warning was given to allow for childcare etc.  D refused to come and made a bullshot excuse for not attending the hens night.

All through this I listened to C vent and get upset, I offered support and all that.  She tells me she wants nothing to do with D anymore, deletes her off socials and everything.

Fast forward to now.  I am really keen to go to a museum exhibit 2 hours away from home.  C says yep she will come with.  Day before, she messaged me saying she couldn't come because she was having problems with her husband and they were going to stay home that weekend and work on it.  I said that was all good, told her I was here for her etc.  I checked in over that weekend to make sure she was ok.  

One week later, guess what pops up on the book of faces.  D tagging C in a post about how they went to that exhibit and has a great day.  

AITA for being pissed at C?  I am 99% sure she lied about having problems to get out of coming with me because she knew I couldn't 'get mad' at her for that.  I feel like she suddenly made up with D and decided to ditch me so they could go the following weekend.  C can be pretty immature and dramatic.  I wouldnt put it past her to lie about it.