My daughter just recovered from this and started back at practice this week. She's 9 and it was an acute injury that caused some distraction of the growth plate. She took 4 weeks off from any swinging or weight bearing on the arms and then when she was totally pain free was released to go back. She's pretty weak after this and having some trouble getting her giants and free hip-handstands back but with time, hopefully will be fine.
At 13, if she has already started her period, she would be a little slower to heal but assuming her injury is due to one acute event, I would assume that it could take about 4-6 weeks of no weight bearing or swinging and then build back when pain is gone.