I think if you want to decline her invitation so that you can start sending the signal that you will not happily remain good buddies as she tears apart your family, that's fine. But don't have it be because "I am still very hurt, depressed, and angry about this."

Have it be based on your principles, and what is and is not acceptable to you within your M. Confidence and assertiveness is attractive, and you need play no games to show this.

M: A really long time.
Crisis: 5 years.
She's still worth it.

Life is never made unbearable by circumstances, but only by lack of meaning and purpose. -Viktor Frankl