Non-renewal of a lease for late rent

[Bob Cameron]

Currently I have a tenant who was 18 days late with rent this month and was wondering what other's opinions are on renewing a lease with such a tenant. The tenant had been late on two other occasions, but both were in the range of 4-6 days. This month I served her with a 14-day notice to pay or quit after the 6th day and she paid 2 days prior to the 14th day deadline. 

The tenancy is up in September and I gave a notice that the lease will not be renewed because of late rent. In addition to late rent, the tenant is not very punctual about meeting to collect rent, has always paid in cash which is not preferred, and has someone living in the unit who is not on the lease, despite having gone over this as a violation of the lease agreement. Would others recommend continuing to rent to such a tenant or cutting ties to avoid things getting worse? 

I am a first time investor living in a multifamily property where I am an owner-occupant of one of the units.

[Bob Cameron]

I am in Massachusetts where 14 days is required by law for a notice to quit for nonpayment of rent. Late fees also are not allowed until after 30 days of non-payment and then I believe you are only allowed to assess for a $50 fee which I believe is one-time and not daily. 

Going forward I will not be accepting cash. But if we were to go to court and she said that she had paid wouldn't it be my word against hers and go nowhere? 

The unauthorized tenant I believe is a significant other. How do you guys go about getting proof that another person is living in the unit? I am sure they are living there because I live there as well but would that be enough in court? 

Thank you both for your responses!