It's impolite not to respect people's privacy.
Marie is supposed to work on a project with the new employee Sandra, and Sandra leaves the window of her Facebook open on her computer.
Marie wants to know more about Sandra.
Marie asks Sandra questions about herself while they work and invites her to hang out at a more relaxed location.
Marie searches on Sandra's Facebook reading her messages along with other things on her page.
Marie forms a relationship with Sandra.
Sandra discovers Marie, and she asks for Marie to not work on the project.