You know, extorting the money from her is probably not the best solution to your problem.
It all depends on the circumstances of the loan. I'm with Rip: if it's money loaned to a GF or wife, it's gone.
If it is a legal loan, you should have legal recourse. Unlike extortion, doing so is not illegal, and you don't run the risk of ruining your life too. Of course, you may not get your money back.