In answer to your last question, she did not sue the government and never would. Beyond that, I will not discuss her personal business.
I am talking about signing a form in agreement not to sue the airlines, in exchange for a taxpayer funded pile of cash. Not about suing the government. It should be a simple mater to tell the truth. You said "My sister-in-law did not want to spend the next 10 or 20 years in litigation. She had kids to raise and hearts, including hers, to heal.", this would imply that she took the cash, otherwise litigation would of never entered the picture. Taking of public funds, should be a public mater. If she did not take any whats the big deal in saying she did not? Odds are however that she did because most people jumped for a chance at the cash, I know, kids to raise and hearts to heal.