Tenant wants to move from upstairs to downstairs in duplex, cheaper to more expensive

[Arron Achey]

Hello all, 

I did look through some previous posts on similar topics and lean towards NOT allowing this but our situation is a little different then I've seen. Our downstairs unit (duplex) pays for pretty much all of PITI and utilities that we are responsible for, where the upstairs is mostly gravy. We just turned the upstairs over, tenant seems to be taking good care of it where maybe some patching and paint needed but otherwise just a deep clean as I would for anyone else.

I'm trying to find the downfall of having her move into a renewed lease, year long, she's a good tenant, and paying higher rent to cover all our expenses while we try and re rent out the top floor. 

Just want to make sure I'm not missing something drastic. 

Thanks in advance!

Arron