How to Support a Partner Struggling with Body Image

My girlfriend has been really down about her body lately. She is very fit and works out five days a week, but she is constantly criticizing her appearance in the mirror. I want to support her but I am not sure what to say that will actually help. Whenever I tell her she looks great, she just dismisses it.

I have tried to encourage her to focus on her strength gains and how much energy she has, but she is very fixated on specific parts of her body she does not like. It breaks my heart to see her so unhappy when I think she is amazing. We are in Calgary and she is part of a few local fitness groups that I think might be contributing to the pressure.

How can I be a better partner in this situation? Are there specific things I should avoid saying? I would love some advice from people who have been on either side of this struggle. I just want her to see herself the way I see her.