Can lawyers do this?

Someone I know is suing their former employer for wrongful termination. I don’t know too much about the details, but apparently her lawyer called her to tell her that the employer had hired someone to follow her as she went about her day: in public and even when she was in her house. She had no idea this was happening, and was shocked when she found out about it. Is this legal (we live in California)? I just feel like this is a violation of privacy.