Poor darling, I hope that her leg heals fast
She could just as easily have hurt her leg from trying to climb out of her pen, or any number of ways. It may not have been your son's doing. Perhaps this could be used to even further teach him how very fragile she is, even if he didn't do anything, kwim
And as for jokes about rehoming your son, I think it was uncalled for myself. Of course, the poster putting one of these>>>>
in the post MIGHT have helped to convey the fact that it WAS a joke.