When to stop responding to excessive tenant complaints

[Sofia Johnson]

I have a tenant who is constantly complaining - it feels like she is LOOKING for every reason to complain. She lives in a downstairs unit so she complains about the noise above her multiple times a day, multiple days a week for 2+ years now. The tenant upstairs and this tenant downstairs do not get along and we've had mediation meetings with no luck in finding peace between them. The amount of complaints are excessive, it is time consuming to address, and we aren't sure how valid each complaint is anymore. 

My question - is there a point where we can start ignoring her excessive complaints? Can we be legally liable if we start ignoring her?