[MovedGoalPosts]

If she has done nothing wrong, why a need for representation. She's got nothing to hide. From the basic facts you have posted this is a case of mistaken identity or even identity theft where your sister in law is the victim. Simply producing her own bank and similar statements, including the birth certificate and any other idenitification stuff she has should be enough to clear up the confusion.

Of course she should merely present the facts. If there is any adverse cross examination going on, that has a legal basis, warnings to that effect will be issued. If she doesn't like what she is hearing, she can decline to comment, until she has legal advice. I'd cross that bridge if it gets that far.