Just got a text message from a colleague saying she was sorry she couldn't make it tonight, but she hopes we all have fun!
So it seems the ladies that I line manage are all going out tonight for a Christmas bash. Funny, no one mentioned it to me!
I didn't think there was any reason why I would be excluded, but clearly I'm not as well liked by them as I thought! 
WWYD though, just ignore it or text one of the others wishing them a lovely evening? I have replied to the text message just saying I hope she has a nice Xmas and get well soon. Didn't mention that I didn't know anything about the night out. I don't want her to feel bad, it's not her fault - she's new!