OK, back again.
My 11 year old broke her arm badly (both bones, displaced, needing manipulation to reset- luckily no open surgery) in August. She had an above arm plaster cast until early September, when it was swapped for a short arm cast (below the elbow) until the beginning of October. She was told to avoid any sport that might expose her to falls or injury (so swimming, dusting, washing dishes etc, all fine, but not roller-blading, hockey or climbing, or anything else remotely fun) for a further 3 weeks. We followed these instructions scrupulously although she was mutinous at times, and she only went back to PE and games 5 weeks after the plaster had been removed.
At the beginning of November, supposedly completely better, she went to a cross country run, took one step, slipped in mud and fell on the arm again, rebreaking it in the same places, although mercifully not so badly.
The orthopaedic surgeon had a jolly good look at her x rays and concluded that she still had "kid's bones" and although there was some displacement the second time, her bone would remodel and straighten in time and did not need resetting. I believe that at this sort of age, how quickly bones mend is very dependent on how mature they are- in tall girls very near or past puberty, the bones are essentially adult's bones, whereas is short undeveloped girls like my daughter, the bones are still very plastic and remodelable (is that a word?).
I would really rather have kept my daughter off sport until the end of the term in hindsight, if only because her confidence about physical things and throwing herself around as much as she did before was badly knocked by the second break and it has taken ages to get her back to things- she only went back to gymnastics last month, three months after getting out of the second plaster (although I must confess that she did ride a very docile pony in December with her arm still in a short cast- naughty naughty).
If your daughter is more mature physically, I would recommend exceeding the physio and doctors' recommendations as much as seems sensible, if only to avoid the potential of this happening to her. It's a fine line to tread between restricting her so much that ends up not getting back into condition, and her risking rebreaking the wrists. Bottom line is, it's unlikely but still possible. If she is the kind of child likely to take a rebreak in her stride, maybe it would be less of a concern for you.