People see this as a two way outcome. Doesn't need to be.
I went online to see if there was a way to get her to live...to maybe eventually see her later, such I've read in this thread, in that prison...knowing it was a potential character that could join my party and knowing i was going to save the grove...Answer is no.
Although, knowing the fact that I've just killed everyone in her castle and she is the only one left... attacking the grove without an army doesn't seem logical...she could flee and i guess could be a reason for her imprisonment... 3rd outcome... and we could eventually meet her in that prison tower.
I haven't gotten into act 2 yet but from the glimpse I've read which is minimal as i prefer to play without tips tricks and spoilers, it feels that it could be a simple solution and plausible outcome with minimal work.
Anyhow, i guess I'll move on and from her being knocked out, I'll kill her and put her in my adventurer's chest.