Hi Linkat , you dealt with it the way most of us would have you feel alright, good , no harm done.
What I am suggesting is this: I have lived half of my life thinking about my "Feelings" and Oh if my feelings got hurt that is a terrible thing. The new direction that I learned now is that we cannot let feelings and emotions run our life. we cannot teach our kids to identify themselves as their feelings.
In my personal experience I have been both the mean girl and your daughter.
Being a mean girl I got a shock of my life when I was called into our behaviorist's office and saw two of my female colleagues who complained how I have been pushing their buttons. I thought of these two girls as my best friends. I was in a new town all alone with a new born baby and thought I could find friends by being friendly and funny. I cried for almost a week. I learned a lot from that unpleasant experience . I wish one of the girls had expressed herself clearly before it got to that point.
So this time your daughter spared her feelings but in the long run as you say if your daughter's intuition is correct than this girl will suffer by being this way and it would be in her best interest if she was made aware of her attitude at this stage.
I have been your daughter many times and have spared many people's feelings , it does not help them and it does not help me. Living life this way ,
Silently over the years it robs you of your peace and joy. The same attitude translates in marriage friendships and professional life.
It seems I am taking it too seriously. To me it is not about this birthdaty party but the bigger question you asked is "Is it Ok to teach our children to lie to spare someone's feelings?"
I am like you when it comes to children I analyze everything.