landlord liability for tenent's dog bite

[Ash Reed]

I would really appreciate any comments here.
I received a letter from a lawyer who represents somebody claims to be attacked by my tenant's dog, and requesting me to file claim with my landlord insurance. I was not aware of my tenant having a dog, and have a no pet clause in the lease. I talked to my tenant, she admitted that she has a dog and her dog attacked somebody a block from my property. I also talked with my insurance agent, and was told my liability does not cover tenant's dog. How should I respond to this lawyer's letter? Should I ask the tenant to move out?

Thanks in advance.