That Teacher saw that Girl I like getting harassed and she didn't do anything about it?

See the Girl I like named Diana was walking in the Hall and then Colby started harassing her.And Mrs.Cobb saw it and all she said was "You better leave Colby Alone!" and she didn't even do anything.It infuriated me and it made me mad so much that I wanted to do something.And then after Mrs.Cobb walked off Diana said "But he was the one harassing me!".It ticks me off that Mrs.Cobb didn't do anything and let Colby keep harassing her.And Diana kept trying to fight him off.I really think I need to tell someone about this incident.Should I?

Mrs.Cobb seems like a teacher who doesn't really care. If you see this happening, tell a teacher or principal in private but make sure no one knows your the one who told on Mrs.Cobb !