Tenant wants rent back

[Ricardo Nieto]

Background: A tenant moved in with her roommate and payed 1100 for the month. The roommate didnt know the boyfriend was moving in and decided to give me her 30 day notice a few days after. She now wants her half of the rent back since she claims she never moved in. 

I think I shouldnt give her back her portion because thats a dispute between her and her roommate since they both have keys and have access to the property. Rent was payed and its none of my business how or who paid it.

This is also during the Covid-19 crisis, so not sure if my other tenants are going to be able to pay, I want to make sure I have my bills able to be payed.

Any tips or am I going about this the right way?