The violent language seems normal from listening to her friends except that DS takes what she says seriously and her friends don't.
Do you mean that her friends also use violent language, or that she's using violent language with her friends as well as her brother, therefore the violent language part of the attacks on her brother is "normal" for her?
It's so hard to know what's up from a few online posts, but honestly, this doesn't sound like typical 4.5 year old behavior to me. Again, I'm not a professional and I only have known the kids I've known, but just from my experience, it's not typical. If you'd listed just one behavior alone I might see it as more typical, but the combination of upset with brother, violent language + violent behavior, and suddenly vivid fears of doing things alone sounds like there *might* be something worth investigating. Not sure what! But I'd try to investigate and understand what's driving the behaviors.
Best wishes,
polarbear
