Terminating month to month lease - please help clarify

[Sarah Present]

Hi all,

I would really appreciate any input on this.  We had a short term lease with a woman who is living in our carriage house, the lease is written that the term is a 3 month lease, with automatic renewal for up to 3 months, month -to month.  Either party can terminate with 30 days  notice for any basis.  The initial 3 months has been completed, and she is now in the month to month portion.  We would like to give her 30 days to move out as our lease states we can.  My first question is: 1) is there a template for a letter that states that for Colorado and my next question is: 2)  Can this be done via email or does it need to be certified mail?  I would be fine with either if I knew I was covered.  3)  is there anything i could not be thinking of in terms of her disputing this?  

Thanks so much!

Sarah