Oh bless her. Same thing happened to me at the same age. I dread having to help mine through the terrible pain of their first really broken heart.
I remember the most helpful thing my parents could do was to keep going normally. Mum persuaded me to go to the supermarket or garden centre with her and got me out of the house once a dayish. That was helpful. It wasn't too demanding but filled time.
I remember her trying to say helpful things, which weren't. The people who did help were those who had been through it and who recognised the pain: a family friend getting divorced; someone else saying "You will survive, but it will take a long time. This is the most painful thing you will ever go through. This hurts like nothing else, but one day you will feel better."
Someone else pointed out that this was a bereavement. My hopes for the future and my relationship had died. I was allowed to mourn and feel bad. That helped.
Telling me to cheer up, or move on certainly didn't help. Neither did "At least you weren't engaged/married. That would be worse!" . Telling me to fake it, go to the hairdressers, meet up with friends etc, because then he might see what he had lost, did help a bit, because it gave me something to do, whilst letting time do its work.
I worked out that it would take a year to get through all of the firsts - first birthday without him, first Christmas etc., and that it was OK to feel sad for that long. I stopped howling everytime I walked down the street and saw a couple holding hands after a few weeks, but you can't hurry someone through grief. Just be there for them, and buy chocolate!
HTH