Quite frankly, I’m not sure what you mean by “reverse shoulder replacement” surgery. It’s laudable that she wants to do some preparatory strengthening, but I definitely agree with Sue that you should consult with her PT and/or surgeon to determine the best resistance exercises for her. Shoulder abduction, horizontal adduction & abduction, flexion and extension, perhaps internal and external rotation, could all potentially be part of the mix. Just clear with her providers prior to beginning a program. I wish her the best.