Could this be child sexual abuse?

Hello all, I really hope to get some useful advice from this issue. I can tell you, it has been relentlessly bothered me for a very long time now. I’ve tried to get a social worker’s help and that lead to a dead end yet I still have this persisting gut feeling telling me not to let this go. It’s a long and complex story but I’ll explain it in a nutshell to my best ability. I also realize I’m asking a general audience that will likely leave me without professional or clinical answers and even if you were, I imagine it takes more than a post to be certain about something of serious nature. I simply want to get an objective opinion from regular people because after such rejections from professionals, I’m beginning to second guess myself and wonder if I should give this family the benefit of the doubt.
I’m a special day assistant and have worked with this particular 6 year old girl with severe autism for about a year. She is nonverbal which means she doesn’t communicate but will voice in a few words rarely. She can say the words eat, no, baby, spin, play to name most. When I began work with her as a kindergartner, she was extremely aggressive, she would hit staff and classmates on a regular basis to gain attention mostly, even when she was given continues positive attention it didn’t help sever this behavior as we’d hoped. She would run away if eyes were off her for a split second, and since I’ve known her she’s worn a tracking bracelet for same reasons reported at home. Mom has accused all of us staff members of abusing her daughter. Every time the girl appeared with bruises on her body or cuts, she would report this to our principal and even went so far as to contact the school district office to continue accusing. Mom is very manipulative and conniving, it has been difficult dealing with her. She demands unrealistic expectations from us to implement with her daughter. For example, she demands integrating more socializing opportunities when she is more than aware her daughter is a highly and unpredictably aggressive with her peers and it’s obviously not safe to keep her within close proximity of the other children. During this time as a 5 year old, she displayed sexual behaviors. The little girl regularly touched and rubbed her privates and still does. She makes gyrating motions while sitting in her chair as if she’s masturbating and she makes distinct moaning sounds as well. There was a time she would also attempt to stick toys in her private region. She got to the point where she would find a toys that vibrate and do the same to receive pleasure from it.
As a 6 year old, her aggressive behavior has toned down impressively although still there. She still rubs her privates and then smells that hand. This girl also comes every day smelling very badly of body odor and repeats clothes often which are old and too small for her, her buttocks are always showing at almost every movement. Earlier in the school year, one of the teachers took her to the bathroom where they saw some spotting in her underwear. The girl points to her privates and says “hurt.” This was reported to cps and after continuous pressing on my end, they opened an investigation. Mother was told about it and she said she’d take her to the doctor but we didn’t hear back for a long time until her teacher asked again. Mom said the girl had a bacterial infection and that is the reason she is touching herself. Later she retracted her statement and says the spotting was from the hot Cheetos she eats at home. They were furious one of us reported them and at a meeting, they went off on the team. They just couldn’t believe they got a visit from the police and social worker and wanted to know when this would stop. Shortly after and quite suddenly, the little girl completely changed, her behavior was spotless, she was compliant and orderly, it was amazing. Mom was also not giving any problems as well. But after a month or so went by, I noticed mom began acting bizarre again and around that same time her daughter also started going back to her problematic behaviors.
It’s been just very odd watching all of this unravel before my eyes. Sometimes I don’t know what to make out of it. I just can’t seem to justify under any circumstance a 5 year old girl with autism knowing exactly what to do with a vibrating toy and exhibiting horribly sexual advances I didn’t even imagine as an 11 year old girl myself let alone at 5 years old. I’m also extremely concerned because she’s highly vulnerable as a child with a disability and I don’t for one minute trust her parents’ judgments either. I can’t help but feel this is happening and I just want to feel validated that I’m somehow right to feel this way or if I’m not, then please give me some reasoning to rather take this with a grain of sand.
Help? Anyone?