I know I'm a lot late, but I know what you feel. Your friend is right that she doesn't need to smile all the time. It's incredibly hard to see her sad, but you can't "fix" her, and she may feel worse if you do. With regards to therapy, that's not necessary what she needs, if you think she's too busy because she doesn't feel she has a purpose, then help her find a purpose in spending time with you. In addition, I'd suggest you research how you can support a person who's undergoing therapy, because you will make more of a difference than a doctor she doesn't know if you learn what a doctor would learn.
I hope that makes sense, I'm always willing to answer any questions, and I shouldn't be too busy coming up soon.