Why aren't you letting the L handle this? That is what you are paying them for and it appears that she will argue for spite no matter what you offer. Next time, take a picture of the car (or whatever the object) with a date stamp and don't even mention it to her. Personally, I would not send the paperwork directly to her, I would let your L send it to her L.
M 46 H 44 D 12 S 8 M 9 T 11 BD 2/15/13 "Makes sense to stay together" 5/12/13 Agree we are 'healing' 7/13 Definitely Piecing 9/13