She’s most likely going to be ruined for the rest of her life. She may be able to forget it, since she is so young, but just like a dog that remembers the feel of the master’s boot it will never leave her. The memory of a male family member causing her pain will last forever, even if it is buried so deep that she never consciously realizes it.
So basically this beast thought his temporary pleasure was worth ruining her entire life. I’m glad he is dead. My only sympathy lies with his victims.
Sadly, she won’t be able to forget it because the family will forever be talking about it. Some (especially since there are two families and being half siblings) may even turn it around one day and blame her somehow for grandpa being in prison and brother being dead.