It does sound like that the entire thing with Dee Barns, was a longer saga, and I can see why that would, from a story and narrative purpose would have been cluttered to have been included in the script. When you are writing, you are cutting things constantly. No great film didn't have a tons of darlings cut out. Movies that don't do that have disastrous pacing.
Secondly, one has to understand, and this is one of the paradoxical problems of biopic films- Stories on film are not real life. Rarely does a real life story, translate 100% well into a 3 act 1-3 hour story for film, with all the appropriately addressed pacing, character development, unfolding just so you it will be great for entertainment.
So you always have a conflict of interest when your trying to sell something under the guise of "based on true events". It's always open to interpretation. - And you really have to question (I haven't seen the film yet, BTW) when someone makes a biopic about themselves to tout their own horn.
I think movies like Walk the Line and Ray, benefited from being made after Johnny Cash and Ray Charles had died. It made it easier to show their grotesque and dark sides.
So I am conflicted about this. It's entirely possible that the film could have worked with a short scene of Dre beating the shit out of this woman, or it could have been used as a plot device, or even be a part of a montage, but it is also possible that it simply didn't make the cut. It's hard to say. I've heard someone else say that the film really paints Dre in a positive light, and if that is the case (he was a gang banger after all) that doesn't bode well for the objective authenticity of the film. But again, as we established before- The conflict of interest is a major red flag.
