Walkthrough and smelling smoke - Letter to tenant, California

[Nick J.]

Hi B.P. Family,

I have a property in Ventura County, California. The tenant has lived there since November 2017, I walked through it in April 2018 and everything was sound and smelling just fine. I recently did a walk through (April 2019) on the property and the second I walked in I noticed smoke in the home, and a cigarette butt in the garage area (that I took a photo of). I'm wondering the best way to approach the tenant to remedy this issue. We do have a clause in the agreement that states there is absolutely no smoking on the property (and if she breaks the terms, we can keep the deposit to remedy). So, she is breaking the lease, however I'd like to ask her to remedy this before having to slap her with legal notices and warnings. She pays her rent on time, and we don't hear a peep from her in regards to anything, really. She's a good tenant except for this issue.

Can I legally ask her in an email to remedy the smoke issue by the next walk through, and also threaten her with official notices if it's not resolved in that same email?

Any tips or advice are welcomed. 

Many Thanks,

Nick