Your kids are probably busy and entertained with inlaws in town. I wouldn't take it personally. K graduation...I remember that well. So cute.
Let me give you another side to your thoughts and I may be out in left field here. My first exh (my older kids dad) and I had a very friendly divorce. In fact, now we say it was a huge mistake and we were just dumb and immature. Anyway, we have always gotten along well. We talk about stuff, our kids and he even helped me through my D with exh. Its always been comfortable and easy to get along with him. I would rather have it that way then the anxiety I feel with this exh. My point? Don't read too much into her friendliness. It may be something triggering thoughts or it just may be comfortable to her and in her mind she may be slipping into the routine. Not trying to be a downer here, but just don't overanalyze...from the queen of analyzing
Me: 46 FWS: 36 Married and Divorced 4/07, Pregnant 7/07,False R 7/07 Baby Girl born 3/08 Kicked him out because OW: 7/08 5/10 He realized what he had and lost. Moved home! REMARRIED 3/14/11!!