Uncomfortable

So, although my XMIL and I remain close, there is one thing I simply cannot do and that is to ever go into her apartment at the senior home where she lives. I did that once and knew I would never go back.  On her living room wall was a huge family picture which I believe was taken in 2009 when her son  married the OW. Even her 2 kids were in this picture. It was like a stab to my heart and I felt nothing but replaced. I had been in that "family picture" for 24 years. That was MY children in that picture, not hers and her children do not belong. 
She asked me if I wanted to come in after we went out to dinner tonight and I quickly declined just stating I needed to get home. As much as she was my "other mother", she would never be able to understand my feelings in regard to that picture. She was married over 50 years to the same man, so I could never explain to her why I simply cannot put myself through that again. 
I did notice though the one time I did go in her apartment that she has the old family picture we had taken 17 years ago in her bedroom. As much as my ex took from me, he didn't manage to keep his mother from still loving me like a daughter. But, I can also understand why some people just distance themselves completely from the entire ex family after a divorce. It probably would make some things easier.