I don't thing ANYTHING is a defense in cold blooded murder. Not even 14 yrs old.
No one really knows
how common child abuse is.
Some psychologists
think many children
create fantasies of grief.
Some psychologists
think abuse of girls
by fathers is frequent, BUT
such an AWFUL crime
that Western culture
can not face up to it and
pushes away truth.
If she was abused,
it wouldn't "justify" her,
but might explain her.