You've been given some really good advice here, and I can't add anything to it.
I know how hurt and bitter you feel right now. It's the worst thing in the world to see your child hurting, and there's nothing you can do to help her heartbreak. (But there is nothing you can do, except listen to her, cuddle her, dry her eyes, and help with the practicalities.)
I've been through this situation with both of my daughters, and know what a tough time this is for you.
But it won't last! Your daughter will get over this in time. (Everything passes.) And you'll look back one day and realise that it was for the best.
I now have two new sons-in-law, and both of my daughters are the happiest they have ever been.
No matter how dark and dismal it may seem to you now, there's always light at the end of tunnel!
Hang on in there, and do what you do best - being a loving mum and nanna.
And I guarantee, that in five years' time, life will have moved on, and all of this present emotional chaos won't matter a jot.
Keep your chin up - and Good Luck!