Is Giving In The Best Choice Sometimes?

So... my mother sent me a text message today and asked if I could come over tuesday or wednesday to take a photo with her family. For their christmas card. I was truly perplexed at first as to why she would even ask. Like, that just does not make any sense to me at all... but then it hit me... She still has this idea we are some perfect family even though we barely communicate. We never have been a perfect family. I was always the kid she had out of wedlock before she met the man of her dreams and had her own little family with him, and thats how it is. That is how it has always been. And that doesnt bother me at ALL. But what does bother me is the fact that my mother does not accept the fact that I am not a part of that image that she wants. I told her that I am not sure if I feel comfortable doing that but I will think about it and get back to her. That is so true, I would feel SO very uncomfortable being in a picture with them. Especially after what a fucked up year it has been. I mean, I cannot believe all of the shit thats gone down with me and her this past year. I just have so much thinking to do. I know it would be the "mature" thing to do and because of that reason I want to do it in a heart beat, so I do not seem like a brat. But then again, this is not about any of that. I know that if I "give in" to this it will just have my mother right up on her high horse again with her thinking she is in control of me. She needs to realize at this point the whole her being in control thing of me is over, and I do not want to give her a taste of what that is like again. I will be treated like shit even more than i have in the past. I love the idea of a family being picture perfect (in the best sense of the word) but If I pose in this picture I do not know if I can look at my self in the mirror without thinking I gave in and did not hold on to my own boundaries. Because I have to set up some boundaries against her. I do not want to get as hurt as I did again. I cannot afford that, I am the happiest I have ever been in a long time. Ever. I just have no idea what to do...