Are guns the problem? Yes and no.
Guns do not make humans more violent, but they do make us capable of being more effective when they are violent.
The problem with this story is drugs and I would bet some other social ills that often tie into drug use.
But if the guy didn't have a gun he couldn't have shot her (obviously). Doesn't mean he wouldn't have still been violent, he might have still punched her, hit her with an object, etc. but she wouldn't have gotten shot.
For the sake of this issue I think it would be good to differentiate premeditated gun crimes and non-premedicated gun crimes. If I am going to target someone to kill them, rob them, etc then I am specifically arming myself and planning to use violence. However if I am not planning to be violent but a situation arises (bar fight, domestic argument, etc.) then there is a likelihood that what would have normally been a fistfight now becomes a murder. Not because I planned to commit a murder but because I now was in an aggressive state and I have a firearm so in my altered state of mind, I might now use it. I remember the story of a murder at a bar in Kaneohe, would have just been a fistfight most likely but the guy pulled out a knife and stabbed the other guy in the heart, killing him. Did the knife make him more aggressive? Probably not but it enabled him to kill the guy where before probably no one would have died.
So the gun isn't the problem, but it also isn't not part of the problem either.
I think the left has this myopic view about how gun regulations will solve the problem and there are certain logical elements to it but it is not a comprehensive view of the overall problem.