Dear member,
What is happening at your company is horrible. Any woman, whether employed as a regular employee or as a casual, temporary, outsourced employee, has the right to live with dignity. If salacious comments are made against any woman employee, it merits investigation.
Before providing a solution to your challenge, please confirm what you mean by "third-party complaint."
Now, coming to the solution. Yes, the matter falls within the purview of POSH, and nowadays it is not ICC but just IC (Internal Committee). You may call the complainant to your office and ask her to gather material evidence. For this, she may sit reasonably close to the employee and record the conversation. Most Android phones have built-in apps for recording, and additional apps can be downloaded as well. However, instruct the woman employee to check the maximum duration for recording. If the comments have a sexual undertone, advise the woman employee to confront the individual making such remarks. While confronting such employees, she should be polite but firm and should not lose emotional control. Let her not reveal that the conversation is being recorded.
I suggest gathering material evidence to strengthen the case. Once she has incontrovertible evidence, she should approach HR once again with the audio clip. HR can then proceed as per the procedures outlined in the POSH Act.
Thanks,
Dinesh Divekar