Quote - Maddie is rigged hip -> buttock -> thigh right?  Like V3/M3?  If so, then it may be a good idea to include the rButtock/lButtock bones in your donor rig.  This way, with the skirt grouped as all "hip", then the character's buttock bones can deform the skirt as the legs are moved.  The thigh bones will not, but there's nothing to be done there except with posing handles.

oops, ps:  When testing, rather than run entire poses at first, just check each joint, bending it one direction at a time.  Save the full-blown pose testing for last, except maybe just for grins.  You can only fix joint parameters one at a time anyway, and when you apply a full pose, it's harder to identify which joint and which bend is actually causing a problem.

Yes correct. That is Maddie's rig. Will include the r/lbuttock bones next time.

Thank you Pjz! You're always very helpful and patient.