Can a tenant allow access of a detached garage to others ?

[Hien T Pham]

Can a tenant allow access of a detached garage to others ?
I manage a 10 apartment complex in Buena Park CA where the garages are in a different areas. One of my tenants is on section 8. The father of her daughter came out of prison recently so she allows him access to her garages so he can hangout out there. He invited his gangster friends over too, at night. During the day this guy go inside her apartment. I have to go there and stay up all night like a security guard to prevent these scary gathering and it's taking toll. I plan to give her a 90 day notice on April 1st when the lease ends. Could someone advice ?