Poor dear probably stuck her hand out in an attempt to catch herself (as one does). I did the same thing in college. Hopefully she’ll feel better soon and heal up nicely.
It is a clear human instinct, a kind of reflex. Over time I have heard various people breaking or bruising 1 or both wrists after trying to catch themselves when falling (of all ages). I once bruised an underarm while trying to catch myself in a bike accident (I also instinctively wanedt to prevent to fall with my whole weight on a child who ended up under me in the accident). But in this case in combo with her age and such it will probably take more time to heal. Best wishes to Silvia.