From a conceal carry perspective I think she will be in the clear here unless that Wal-mart had a sign outside saying no concealed firearms allowed inside. If that's the case then she's screwed. But I don't think Wal-Mart restricts conceal carry in their stores. Regardless of the fact they're fighting over a spiral notebook they were under physical assault. Pretty sure she's in the right there. But that's the thing... even if you follow all the rules and laws, if you draw your gun on someone you're gonna need a lawyer.
But I can't help but see a case like this where there's a witnessed assault, a witnessed person drawing a firearm at a Wal-Mart and then compare that to the young man, John Crawford, in Ohio who picked up that Air Soft gun off the shelf and was just talking on the phone with his girlfriend when the cops shot and killed him. I wonder how the police responded to this call(assuming there was one). Never know how police are going to respond. And while I respect the job they do it's a steadfast rule in our house to NEVER call the police. Handle the situation ourselves no matter how dire.