I'm sure there's somewhere better to post this but putting it in AIBU for traffic.
I have 2 DDs, ages 16 & 14. 14yo is stronger than her sister (this is relevant). They've never got on well due to personality clashes and also 16yo has mild ASD so needs to be treated differently in some ways. However, over the past few weeks it's just got so much worse. DD2 seems to have a problem with DD1's very existence, and frequently assaults her (DD1 usually doesn't fight back, and she's not strong enough anyway). Yesterday DD2 actually threatened to kill her - she wouldn't actually go through with it but DD1 takes stuff like that literally. She doesn't respond to discipline and if we try she often assaults us and says she'll kill us too (again, she wouldn't, but it's the principle).
I love DD2 very much, but things can't go on like this. I'm really not sure how to handle it. Has anyone resolved something similar and have any advice??