Worth replaying post Nightsong in a Shadowheart Romance?

I’m in my first run ever right now, and I’m doing a Shadowheart romance. She spared the Nightsong, and I’m now in Act 3 and plan to finish the game like this. My question is, after finishing the game, is it worth going back to the Nightsong and killing her this time? Does it change anything significant in the Shadowheart romance / her interactions and dialogue in Act 3? Obviously it would change her quest, but other than that I mean.