I would want to be really clear with myself about what I was needing from emailing and receiving a reply and then boil it down to that. In other words, something short and clear that does not take time for her to decipher and think through a reply. I wouldn't look for more than wanting some kind of connection--a couple or few sentences saying how I felt and what I was looking for.

There have been times when real therapy has happened through emailing my therapist, but it's been a bonus. I would think for the holidays to look for just enough to maintain a connection would be worth it for both of you.