Reminder of month to month tenancy?

[Carrie Nevins]

My current tenant signed a lease beginning November 1, 2017 through May 1, 2019, however she paid for the first 12 months in advance. I am thinking of sending her a "friendly reminder" letter just stating that November 1 she will begin paying monthly, yada yada, and reminding her of the late fees and so forth. 

Is that appropriate or should I just see what happens? Also, should I just keep it informal? I was looking online for a template, but this scenario is an uncommon one.

Thanks!