I'm really sorry to hear this, do you know what stage the cancer is? If they've caught it early the hysterectomy will get rid of it & they will probably give her some sort of chemo as a precaution.
My MIL had ovarian cancer that had spread to her lymph nodes 2 years ago and had a full hysterectomy and 2 rounds of chemo. She's now been clear for a year although she did have to have further surgery as she developed a hernia which is common with hysterectomys. She still has to have check ups to make sure the cancers not back but other than that's she's ok.
I know it can be a tough and scary time but give her loads of support & make sure someone goes with her to the appointments to make notes as they will give her info that she will forget.
Any questions write those down too and go through each one with the doc, as you will forget them when you go if you don't.
I'm here if you have any questions that I can help with, otherwise try not to stress & remember to look after yourself too.
Take care x