Annoyed by the Fed

I've seen this several times and enjoyed it, but (beware possible spoilers)
I was always annoyed by the Fed, but this time I couldn't overlook the things she was saying to Allison about why she had to cooperate with the investigation. They were ludicrous and insulting to the audience.

First, how can a person possibly be charged with "accessory after the fact" in a supposed murder that happened before she even met her husband? They can't just assume she knows something. Especially since it was obvious at that point, Allison had no clue there even had been any possible murder. So, if she comes up with nothing and they prosecute him, she can be charged under the assumption she was covering up? How about the aspect that you don't charge civilians with doing the job of law enforcement officers? Or the fact that she would be completely endangering herself by snooping around? Or that a wife generally cannot be compelled to testify against her husband?

I know there has to be suspension of disbelief, but this aspect of the movie was so ridiculous that it made me angry.

/end rant