What do I do if tenant is not abiding by the lease agreement?

I have a tenant who signed a one year lease. In the said lease, no other persons are allowed to live in premises at all, no animals are allowed at all and lease states she must maintain all smoke alarms during the stay. Tenant allowed someone not listed on the lease to move in and removed smoke alarms from home after being asked to reconnect. They were left undone for 4 months. I served her with a notice to quit and the day I served her, I also found she had a cat inside the home. Tenant contacted an attorney and the attorney sent me a letter stating she had replaced the alarms and no one was living there outside the lease. I have recordings of admission from tenant of the other party living there as well as pictures and screenshots from other party admitting to living there.