What is the advice and what are the necessary measures to be taken when exposed to betrayal by a colleague, which includes sending emails that defame one's reputation and describe the girl as "promiscuous"?

Our advice to the sister is to adhere to the rulings of Sharia concerning women and to avoid mixed-gender work environments due to the Sharia prohibitions they entail, such as looking and private seclusion (khalwa). If she is compelled to this work and cannot find another, then she must adhere to the Sharia regulations for a woman's going out and working. These include: wearing the lawful hijab, not speaking in a soft and alluring manner, and not speaking with non-mahram men unless necessary.