They address the fact of her accusing Lumumba in the documentary. She says that the police went through her phone and found a text message exchange between her and Lumumba in which Lumumba gave her the night off of work and she replied, "We will see each other later, have a good night," meaning she would see him at her next scheduled shift but which the police interpreted as the two of them making plans to see each other the night of the murder, and that the police were persistent in their pursuit of this idea. She then says that a police officer started slapping her in the back of the head, yelling, "Remember!" and that she "broke" and described Lumumba being there when Meredith was murdered (which of course means that she was also describing herself being there when Meredith was murdered). It's horrible that she accused Lumumba, and I think that the way that she describes it in the documentary deliberately minimizes her culpability in his life being upended and him being jailed, but based on what's in the documentary it seems like she was really immature, even for a 20 year old, and stronger people have broken during police interrogation over a lot less.
As for her not being considered a suspect before being brought in for questioning, Mignini himself says that he suspected her before he even questioned her because she wasn't behaving in a way he thought she ought to be.