Badeline represents.... I dunno... anger? She has to accept that she has anger? Is that what it's about?

I didn't relate to it

How does hugging my evil twin and climbing a mountain with her tell me how to have less anxiety

Because it made her more confident in herself, beating a mountain is a pretty big accomplishment and a great booster of self-esteem

I guess I can see that? Doesn't the whole game say that climbing the mountain doesn't actually mean or do anything, though