How do you prove you sent a "Notice to Vacate?"

[Vincent Plant]

So my rental property's lease is coming to an end on 7/31 of this year. I want them out and do not wish to renew. The lease states that I must give 60 days notice to the tenant if I do not wish to auto renew. 

My tenant is very open that they do not wish to leave. 

So, I sent a certified letter containing a notice to vacate. This was unsuccessful, she never signed off on the letter. 

Sure, I'll email it, hand deliver it, whatever but do I need to do anything further to PROVE that I sent this notice? Obviously she won't sign it. Even if I place it in her hand how do I actually prove that I gave it to her. Or do I even need to take it that far?