Lisa may offer the whistleblower full confidentiality because they are not a suspect

Lisa should explain that she will try her best to keep the whistleblower"s identity confidential.

Lisa should state that she will not be able to keep the whistleblower's identity confidential because all information must be disclosed to management

Lisa may promise the whistleblower full confidentiality, even if she knows her statement is untrue, because the lie is ultimately beneficial to her employer.