Charging a "Premium" for Month to Month

[Jonathan Liu]

I purchased a duplex and inherited my tenants. I recently raised rents and the tenants were fine with the increase. One of them signed a one-year lease, but the other side does not want to commit to a year because she works far away and isn't sure if she wants to move within the year. My property manager told her there would be a month to month "premium" of $50 a month. However, the tenant says she cannot afford the premium. My property manager does not want to press for the premium because she thinks it will be difficult to replace the tenant this time of year. I don't want a vacancy over this $50, but without the premium, I don't see any incentive for the tenant to sign a long term lease.

What should I do?