Yes, it's denial...but judging the woman for it while she is grieving is way harsh. She also said he had just started being good...and then this happened. She sounds like someone distraught...not someone literally thinking the cops are why her son died completely.
I am sure she is more mad that the cops are the ones who ended up killing him instead of "helping" him....which is a concept very common in poorer communities...that the co[ps are not there to help the people but that the people are enemies.
No one in that neighborhood likely ever felt "safer" because they saw a cop drive by.
That much needs to be understood to understand where she is coming from.