Would those who object to giving their mum a lift to her grandson's wedding feel different if she asked herself?
Also, where does the idea come from that anyone has a right to be invited to a wedding, and is 'excluded' if that doesn't happen? People say the young are entitled, but this is, to me, the height of self-absorption. Nobody should feel they have to have a wedding of a particular size, with a set number of guests. They are expensive affairs, and these are difficult times. I don't know if the bride's parents are paying (in which case the SIL won't have any say, as MOTG) but regardless, I am astounded at how many people seem to feel that it is a slight on the OP that she and her husband haven't been invited to a nephew's wedding.
Having said that, the OP hasn't said what her views are, or what her husband's are either - it would be helpful to know.