Oh and gt I meant to say. I had a very similar break to your mum, although I just, by the skin of my skin, didn't break thought the skin. I too had a night before they could operate, because it happened on a Sturday afternoon, which I spent very drugged up iirc. It was very painful. And I thought it would stop hurting when they had fiddled with it and put the cast on, but it didn't. She will be in lots of pain and very uncomfortable so make sure she gets lots of gentle cuddles and pampering.
Also my hand on that side got very dry and I remember someone bought the Clarins body lotion for that hand and it was lush, the smell of it now always reminds me of my injury.
And my other pearl of wisdom
is, they will probably offer physio after, make sure she follows it through and does all the exercises. I didn't and you can see where my hand muscles don't curve out from the wrist up to the little finger like they do on the other hand and I still suffer with it quite a bit if I am tired or run down, it gets more painful than I ever admit. I think if I had stuck with the physio it would have built it up more effectively.