I’m sure that you know that the Last Supper was Christ’s last meal? He was crucified the next day. Did He, or did He not see His Mother as he carried his cross? Was Mary present at the base of the cross when Christ spoke to Her and John? Why is it a leap for you to believe she was present at the Last Supper? Or are you going with the Da Vinci’s version?
He knew it was His last meal. That’s why he said, “Everyone who wants in the picture get on this side of the table.”