Teenage daughter smoking pot

So I recently found out that my 16 year old daughter has been occasionally smoking since October. It’s legal here in Canada but I have never smoked anything, ever, and had never introduced this to her. When I confronted her, she said that it was for her mental health because she has been struggling. She’s been having mental health issues since she was around the age of puberty. How should I go about this? Should I discipline her?