just explain to her what hormones are and how they all go crazy before you get your period. and it's totally normal to feel all crazy inside and have mood swings, change in appetite, etc. and be sure to remind her that it's hard, but when you're feeling all crazy you have to calm down and remember what's going on inside you
You can explain it but don't program her to go crazy because of her hormones because it isn't always that way. I didn't "go crazy".My friends didn't either . We were cool and calm about most things.
But I did have some awful cramps. And heavy bleeding. But, I didn't react badly to it.
Give her a positive pep talk and let her enjoy being a woman.