Undervalued Renter for new investment

[Walter Melnyk]

We just purchased a duplex where the owner lived in one, a tenant in the other. We will rent out the owner unit at $1250, but the tenant is paying under market rent at $900 on a month to month lease. We ironically happen to know the tenant, but not a close friend and she seems to take very good care of the unit. Is it best to slowly inch up the rent and eventually get to FMV or to give 60 days. notice of a rent increase to $1250 where she will most likely not be able to pay it (she's on Social Security)?