So question, I've seen posts about people sending her fan mail and what not, and I was wondering if you knew where fan mail can be sent for Katie?
Ah yes! I can help. It is through her agency:
20 Golden Square
A couple more pointers/suggestions that I picked up from a friend. Apparently she answers fan mail once a year so there is the advice to get your fan mail out soon because I believe they start filming Supergirl again in a couple months.
If anyone knows any more information, feel free to add to this or shoot me another ask or message so I can update here!