How to beat Garen

Hello I play Camille sometimes and I know she’s a counter into Garen but I don’t UNDERSTAND how’s she a counter into Garen . Someone please enlighten me and tell me how she counters Garen:

a) laning phase

b) mid-game

I’m assuming she just outscales Garen in late game and wins around teamfights. Correct me if wrong and thank you in advance!