Tenant fails to notify landlord about guest

[Jade Wong]

My tenant moved in about one month who has been having her boyfriend staying overnight every weekend since week one. In my lease, it states "Residents may have a single overnight guest for no more than three nights per calendar year." Clearly, we were strictly trying to avoid unauthorized tenant to move in. We just wanted to rent to sole tenant. 

I confronted her right after we found out the case and asked about her guest. Her response was "as long as I pay you the rent, I can do whatever I want to." I confronted her again with the highlighted rule in our lease. Her response was "I didn't see this when signing the lease." I then asked her to continue following the rule and notify me when she has guest over, she said "ok". However, she still has her boyfriend stay overnight every weekend. What should I do? Thanks in advance!