Because winning in court is no guarantee. In the real world, it's usually a lot easier to take the money and run than spend years and years fighting in court for something you may not ever see and even if you win, it won't be all that much more than you already had offered to you.
It's a huge gamble. The risk/reward ratio simply does not justify the decision to spend years in court, filing suit, going through appeals, etc, for virtually no gain.
We all know she's no saint. There's no guarantee she wins in court. It makes far more sense to take the money and run than fight for years and years with little to gain.