Rent Increase Notice- owned property 4 months

[Matthew Keyes]

Closed on a property in march- 3-unit fully occupied.  They were all midway through their leases which were transferred over, new leases were not signed.  I just gave a tenant 60-day notice that I was raising rent as her lease ends 8/30/21.  She informed me that she has been there 3 years and needed to notify her 90-days prior.  I was aware of the 90-day period but was not aware she had been there for that length of time.  Do I have any options, it is not feasible to allow her to renew the old lease as it is $400/month under market.  I would be ok extending her lease an additional month if that is a legal option.  Thanks in advance!

Best,

Matt