i would call this person and tell them before hand all the challenges you will be experiencing and get her to ok the job (in writing) before proceeding forward.
i would load the quilt and stitch complete around the scallop across the top (about a 1/4 inch so it can be hidden in the binding), then i would stitch down the scallop completely on the right side, then i would do some basting stitches on the left side as you work.
this will allow you to remove the left side stitches to ease any fullness or other issues you might experience.
i would do the borders in sections as you go to ease fullness and to try and prevent any distortion.
but again, i can not stress this enough, you need to tell this person up front and they very well could pull this border off and sew another on - i would certainly want to do that if this was my quilt instead of risking the distortion that might occur because the scallops are already cut.
about once a week we see people post here that the LA made a mistake and didn't even bother to talk to me about it first before quilting the quilt.