As others have already said, what she's saying is not really correct.
I can't talk for depression, I have BPD. My relationship is pretty normal, I have no problems in my professional life, I have friends. If you don't know me for years, you won't notice anything out of the ordinary. I can function perfectly fine if I need to. Yet, I struggle daily with for example tons of extreme mood swings. I don't let everyone know and can keep it together enough for them not to notice if it happens around people. But I still have a very real problem and meet almost all diagnostic criteria of the disorder, so I'm pretty sure I do have what my therapist has diagnosed me with.