Maybe I'm just reading between the lines by your post, but it sounds to me as if the family was making a statement by forcing her to participate in the bouquet toss? If so, then yes, they were totally out of bounds. And infantile.
Why do people wait until the actual wedding - or funeral or hospitalization - or any other major event to make their case. If they are against this engagement, they shouldn't haul out their feelings during such a public arena as a wedding reception. Sheesh.
Your friend should now be duly informed of the kind of antics she can be in store for her own wedding - let alone the rest of her life with this man. She can either play their game and fight back or she can rise above the pettyness and be an adult. I'm glad she did the shrug and got up for the bouquet even though I think she was right to sit it out. It was the graceful thing to do.
I hope her fiance was supportive and agrees that his mom was out of line.
You want the 2 cents in the bag, or you want to cary it?