If you don't want to decline her invite...then don't decline it...
Go, have fun and be authentic. If, as you say, you don't mind how this plays out, then you have nothing to lose. You may as well enjoy each other's company in the mean time.
Me 50 H 48 S 23 S 21 D 19 Together 31 years Married 25 years Separated April 2009 Reconciled 2010 Separated September 2017