Unjustly accused of being bad neighbor

[Lunar]

I live in a house converted into a duplex both unites are rentals. A MIL downstairs being rented out as separate unit. This neighbor, even after we have repeatedly asked her to let us know if we are being noisy has now complained in writing to the landlord. We don't have parties or anything like that we just live there. the unfortunate thing is that the layout of the house puts her bedroom underneath our living room. We watch TV and sometimes have conversations there but nothing over the top. I feel unjustly accused and find it rather offensive that she couldn't even say something to us in person about it. I want to know if this puts me in a bad situation with my landlord? What can I do about to counteract it? I have lived there for 6 years and had 3 other tennants live there and we had no problems with them. Everything I have read says noise complaints have to be excessive and reasonable. She is anything but reasonable. A whole host of other issues too. Making up lies to the landlord to make her look inncoent and the victim. Frustrated....