Stepdaughter threatening baby-should she still be allowed here?

My husband and I have been together 5 years, married 2. We each have daughters from previous marriages. Mine is 9 and his is 10. My stepdaughter lives 7 hours away and my husband travels to her every other weekend. When she has long weekends, holiday breaks, or summer break, she comes and stays with us. She has had a very difficult time adjusting, I think mostly because her mom has done everything in her power to turn her against us. My stepdaughter acts fine when she is physically with my husband or staying with us, but when she goes back to her mom's house she turns into something else entirely. My husband tries to talk to her on the phone every night, and she curses, tells him she hates me and my daughter, and says every time she's here acting like she's having a good time she's just lying. She's said some incredibly hurtful and downright concerning things. My husband has asked his ex to take her to counseling, which lasted about 4 sessions. She will no longer take her. I'm currently 18 weeks pregnant. Last night, my stepdaughter, in a fit of rage on the phone, told me husband she wants to "punch the baby in the face until it's dead". She has made threats in the past to me and even one in passing towards my daughter. We have done our best to have discussions about this behavior with her but this has been happening for so long, and her words are becoming more hateful by the minute. I love her, and my heart breaks for my husband who truly wants to be nothing but a good father, but I can't sit idly by and act like it's okay to threaten to murder a newborn. It's just not normal. Her mom seems to think we're the problem, and refuses to get her daughter help. There's a big part of me that just doesn't want her in my house or anywhere near the baby once it's born. We've tried so hard to get through to her but she is so angry all the time. At what point do I need to protect my family from her and cut off our relationship? I feel so confused.