Unfortunately, everyone's mental health battles are different to another's - of course.
The brain is a complex thing, and unfortunately mental health still seems very much a sensitive topic to talk about for many - but it's getting there.
Would your daughter be open to having a conversation on the phone to someone she doesn't know to discuss what's on her mind (if she hasn't tried already/if you have haven't recommended already)?
If so, I'd be more than willing to provide some contact details of some respected charities (not the Samaritans) I give to certain service users whilst volunteering for an emotional support organisation.