I solved the murder and Tova only lost one daughter so far. I know from previous times, she is going to take her own life and leave a note if two of her daughters get murdered during the Blood and Ice quest (or similar).

Now Muiri in Markarth did the black sacrament and wants Nilsine, Tova's only remaining daughter, dead (optional).

If I kill her, will this trigger events for Tova to die as well? This would also eliminate the whole family Shatter-Shield.

Writing this, I come to a conclusion and not going to kill her is the better option. After all it is all about pride and relationship, no harm done here.

http://i.imgur.com/fDqsssw.jpg

p.s. and I am Torbjorn's favourite drinking buddy