Because she wanted to make a duel against the doctor, not a personal vendetta for killing her father, it was a matter of honor because a human kill him instead of her.
For adventure purposes, yes, all story need it.
The other is, be trapped in another anomaly, but most of the time there is evil people doing bad stuff like controlling bodies, so yes.
I have this in mind, That's why I ask about the Breen in other post, but to be honest, I think when more you know about the Breen, more lame it becomes and works more in a mysterious way than a strong antagonic faction.
Because she wanted to make a duel against the doctor, not a personal vendetta for killing her father, it was a matter of honor because a human kill him instead of her.