[@RiverMaiden]
Zachary has no problem with her spirit, and part of his magic analysis ability would tell him that her spirit isn't emotionless, just very good at hiding them, and that she cares for Mary.

As for Mary's antics, they amuse him as long as she doesn't actually try to get him involved too much, although he may end up involved from time to time for one reason or another and may even help out.

EDIT: Actually, I was thinking that she miscalculates her current one, and when Tiamat catches the boulder, she falls off, only to have Zachary standing in the right place at the right time (using his ability to predict her landing spot) to have her land on his back or something.