Angelic, I'm glad that you started a new discussion about this.
It's really hard to watch a friend suffering but bear in mind that, when we're grieving, we take great comfort in our friends being their 'normal selves', rather than extra kind or overly concerned.
Apart from trying to get her to see her GP, just carry on with the things you always do, like trips out and chats, whatever you used to enjoy. Don't treat her differently or like an invalid. If she talks about how she feels you can reassure her that it's a natural phase and she won't always feel that way.