A manager wants appropriate action taken . . she states she overheard and saw a chat that an n/e employee talking about her (negatively). The n/e employee said she did not write anything and did nothing wrong. What action should I take.

A manager wants appropriate action taken . . she states she overheard and saw a chat that an n/e employee talking about her (negatively). The n/e employee said she did not write anything and did nothing wrong. What action should I take.