Tenant filing suit for security deposit from a year ago :/

[Jeffrey McKee]

Hi All, I have a tenant who has come back to me requesting her 400 dollars of the 1200 dollar security deposit. She was 1/4 roomates and did pay 400 of the 1200 deposite. They all vacated the property early due to covid and I allowed it, but did not charge them to break the lease.   I was able to fill the vacancy without any vacancy loss. 

I am learning the hard way that I needed to provide an itemized statement of what I was to keep from the deposit and that it needed to be done within 30 days of vacating. I am well past the thirty days and she is threatening to file suit. I plan to just give her back her 400 dollars to stop her from filing. What document can I have her sign to ensure she does not ever try to sue me again. 

I had the property professionally cleaned for 414 dollars and have an invoice and told her she was only due back a percentage of the deposit.  She suggests that was not the case and is due back the full amount she contributed because I failed to give her an itemized statement. The law seems to be on her side. 

P.S. The tenant is now in law school and feeling very empowered :)