Sorry to hear of your daughters cancer. Yes she should have a will. She should also get a health directive done.
When my dad got a massive bowel infection, doctors wouldn't touch him unless they saw the written directive. We had to go home and get it so they would give him antibiotics for goodness sake. He was palliative though and perhaps your daughter is not anywhere near that stage but it is good to know. Dad would never face his mortality but between a nurse and myself we got him to agree to a directive. He wasn't happy about it and went in to depression but he came good and had some happy times afterward with his other children and grandchildren coming to visit and he didn't have that worry over his head.
Cancer treatment can be a day to day getting through, you do learn to adjust. Atm you are just stunned as your daughter probably is. Look to the brighter blessings as best you can and work through it all.
We are all with you as support. Hang in there, you got this. <3