So, again, you should think of the characters (not just the main character but ALL the characters) as part of a singular character web. Each of them should serve a purpose in the narrative, or they're there to contrast from the main character. So in terms of the plotline, what purpose does the secondary character serve?
I'm a bit confused with the rifle part - If someone screamed at me while pointing at me with a weapon, I would probably be upset too lol. Other than that, WHY does she solve problems with violence? That's a tendency of hers, but does it reveal her character and flaws? If you present this conflict in specific ways, you can convey her personality better.
Like say someone tried to talk to her about a touchy subject and she responds by roundhouse kicking him in the face. This could suggest that this character is
- insecure about certain things
- does not want to solve problems rationally
- acts impulsively
- is sensitive
and many other things, depending on how you present her interactions.
So I guess what I'm trying to say is, you have a good start, but you need to keep asking "WHY??"
Secondary character is rude and violent to strangers. WHY?
Because she's insecure about her past. WHY?
Because she had past trauma and this is her way of dealing with it.
and so on...