It really broke my characters heart the first time she had to did this but what had be done got done :mellow:
If your character had a heart, then she wasn't cut out for the DB in the first place. Savlian summed it up nicely, as he always does on this subject.
To me, there only seems to be 2 ways to rationalize the questline through to completion.
1) Your character is just as psychotic as the rest of the Cheydinhal DB. Kill away.
2) Your character is an infiltrator. This is perfect, since your goal is to eradicate this hive of pestilence in the first place. You're probably still psychotic, but with delusions of being a Saviour of some sort. Whatever. Kill away.
I believe that The Night Mother is Mephala anyway, so regardless of how you go about completion, you always end up as his/her/it's chesspiece.