First of all it is important to acknowledge that this is not your responsibility nor your problem to fix. As a friend all you need to do is be supportive and make yourself emotionally available if you are able.

That is, I've found very general things like:

If you want to talk about your feelings regarding GUY then I'm here for you and I would love to listen

And:

I am your friend and I respect you and acknowledge you as a person regardless of GUY.

To work a lot better than (co)runinating with friends about breakups and problems (I've done this a lot myself in the past).

More broadly:

It is important to recognise that a breakup in a meaningful relationship is a really tough thing which often includes loss of shared meaning, plans, hopes and friendship.

It is normal for your friend to feel grief and it is not uncommon to deal with it with denial. People who undergo relationship breakup often experience symptoms of PTSD (enough to pass the GHQ‐28!).

So I would focus on two sides - emotional availability and well-being:

• Encouraging healthy behaviour:
• See if she is getting enough sleep and if she is not - see if you can help her make the choice to sleep better.
• See if she is eating healthy and enough. If she isn't, see if you can buy her healthy food for a little while or encourage her to cook together.
• See if she is getting enough exercise. If she isn't see if you can go work out together or find a nice exercise class.
• Make yourself emotionally available:
• Acknowledge her feelings and promote a feeling of safety.
• Be non-judgmental and emphasize you are on her side unconditionally on this.
• Make it explicit that if she wants to talk you are there for her.

(Note: I based a bunch of this on research - I explicitly did not want to clutter my answer with scientific reviews - if anyone finds them helpful or would like to contest a point I've made - I can gladly provide them)

First of all it is important to acknowledge that this is not your responsibility nor your problem to fix. As a friend all you need to do is be supportive and make yourself emotionally available if you are able.

That is, I've found very general things like:

If you want to talk about your feelings regarding GUY then I'm here for you and I would love to listen

And:

I am your friend and I respect you and acknowledge you as a person regardless of GUY.

To work a lot better than (co)runinating with friends about breakups and problems (I've done this a lot myself in the past).

More broadly:

It is important to recognise that a breakup in a meaningful relationship is a really tough thing which often includes loss of shared meaning, plans, hopes and friendship.

It is normal for your friend to feel grief and it is not uncommon to deal with it with denial. People who undergo relationship breakup often experience symptoms of PTSD (enough to pass the GHQ‐28!).

So I would focus on two sides - emotional availability and well-being:

• Encouraging healthy behaviour:
• See if she is getting enough sleep and if she is not - see if you can help her make the choice to sleep better.
• See if she is eating healthy and enough. If she isn't, see if you can buy her healthy food for a little while or encourage her to cook together.
• See if she is getting enough exercise. If she isn't see if you can go work out together or find a nice exercise class.
• Make yourself emotionally available:
• Acknowledge her feelings and promote a feeling of safety.
• Be non-judgmental and emphasize you are on her side unconditionally on this.
• Make it explicit that if she wants to talk you are there for her.

(Note: I based a bunch of this on research - I explicitly did not want to clutter my answer with scientific reviews - if anyone finds them helpful or would like to contest a point I've made - I can gladly provide them)