Tenant heading for rent arrears

Rent Arrears

I have a tenant who is struggling to pay the rent despite the fact its mostly paid by housing benefit. Currently she pays the rent 2 weeks in arrears but this month failed to pay all of what she owes and I think it's the start of a downward spiral. She now says she's not going to pay any more rent until some damp work is done at the property. I commissioned a builder to do this work on the day she pointed it out to me, and work is now underway. Basically I think she is stalling because she can't pay the rent. What can I do? Incidentally, the tenant has her boyfriend living at the house although she specifically asked me not to put him on the tenancy agreement. I suspect he may be claiming housing or some other benefit but don't know for sure. I feel she is in breach of the tenancy agreement which states only she and her baby are allowed to live there. Do I have any options?