Patellar instability

My sister had a motorcycle accident two years ago (she was 16) and hurt her knee. She went to the doctor who diagnosed her with patellar instability and said she would need surgery but that she would have to wait a few years. After that her knee would start to really hurt every now and then so she went to two other doctors who also said she had patellar instability and would need surgery. But one one of them said she has to wait a for surgery while the other said surgery while she is still young would mean better chances of her knee getting back to normal. Please could you give us your opinion, we're trying to avoid surgery so is there an alternative to surgery for patellar instability? If surgery is needed which would be better: surgery while she's 18 or when she's a bit older?

Thank you very much