SIL threatening me.(long)

So a little back story. When my SIL was pregnant with her first kid her boyfriend broke up with her n was with other people. He came back after the baby was born. During that time he raped one of my best friends(lets call her D). They were drinking n he took advantage of her, took her virginity, n left her at his friends house bleeding by herself. When he got back together with my SIL he told her my friend had sex with him n how she tried so hard to fuck him etc. So from that point on no matter how many times i tried to tell her the real story she believed her boyfriend. Fast forward almost three years later. I'm currently living with my SILs parents with her brother(my boyfriend/baby daddy) n she knows im good friends still with D n hang out with her as much as i can. Well over a week ago i was going to have D come over, i asked my MIL if that was alright because its her house n itd be rude of me to have whoever over without asking. She said thats fine n i should hang out with my friends. Today i get a text from my SIL telling me that she has no clue why i thought itd be acceptable to have D in her family's home n how even if she finds out D was in the drive way 'so help her god END OF STORY' as she put it. Now thats a threat to me. She threatened her brothers pregnant girlfriend because i wanted to hang out with MY friend who was raped by her piece of shit boyfriend. Am i in the wrong for being upset n does she have every right to threaten me this way?? She has a bad temper n has been known to fight with girls her boyfriend has slept with(hes a huge cheater but she won't leave n has two kids with him now) my friend D is 100% the victim but has gotten threats from my SIL for 'being a slut n sleeping with her boyfriend' even though he raped her n they werent even dating at the time, n my friend was trying to explain exactly what happened. Is this okay n im just hormonal n pissed about it? Or is my SIL the one in the wrong?