Mai wins round one when she traps Shirley in a sunroom, which is way too hot and she has to surrender.
But Mai gets told she has to be out of the region by Christmas.
That is, she has to break up with Santa.
Shirley overhears this, and decides to help Mai in secret.
For various reasons, Shirley is unable to help. The best she can do is give them a little time alone for Mai to say goodbye, and even that only at the end of the line on Christmas Eve.
But Mai can't bring herself to say it.