Gumby, the only thing I can think of is if both she and her parents think she's "normal," they why isn't she living with them? Are they in another country? Being that she's on a work visa and can't keep a job, she should be sent back. If she's so dead set against getting help, there's not a thing you can do! Your sister-in-law has to recognize the fact that she needs help and then have the willingness to change her mindset before it would do her any good whatsoever.

My main concern is for your wife's and your relationship. That is your MAIN responsibility. Nothing else in this life should be nearly as important as taking care of your marriage... and kids, if you have any. This added responsibility that is so disruptive can only add stress to your marriage.

Take this from a person that knows. If you want details, all you need to do is ask.

Good luck!