It is indeed liberating to let go and let God and the universe take over.
It took me years but today I can "smell" a codependent snag when I see/hear one. Nope, not taking the bait anymore.
We are older and wiser and maybe a little bruised and tossed from the journey, but when that lightbulb moment comes, we finally "get" that somethings in life are just not ours to control.
I will keep your niece in my prayers, that one day soon she also gets a lightbulb moment and realizes that she can make good choices and live a better life.
Hugs from my heart to yours.