I own two semi detached houses together - can my partner on benefits move in next door?

Obviously this is a unique, and strange one. But my partner who receives Universal Credit and PIP needs to move out from her mother's soon as she's downsizing.

Anyway, as it happens the property next door to me which I also own (two semi-detached properties) is having the tenant leave in 2 months. 

Could her and her sister move in and pay rent to me? We are in a relationship but do not live together or share finances. The rent would be official income to me, taxed, etc.

Obviously there's a giant, gaping conflict of interest, as she is literally a party wall away from me, but officially separate properties.

She is delighted at this opportunity because she knows with me being her landlord she will never be forced to up and leave. 

Before anyone asks, she can't live with me as my brother and his young son already do, and she has a dog who doesn't like children.