How to handle a problem autistic child in the neighborhood?

I'll try to keep this as brief as possible, but believe it's important to offer some background. There is a family living two doors down from me that has an autistic 13 year old daughter. I understand that the child is impaired, but she is an absolute terror in the neighborhood. When my daughters (12 & 14) get off the school bus, she screams at them to get off her street. When they ignore her, she escalates, sometimes even confronting them and wagging her finger in their face. She doesn't seem to comprehend that they LIVE on her street and that they have to go past her house to get to their own. She rides her bike around the neighborhood taunting other children incessantly, following them and refusing to stop haring them. When they try to ignore her, she begins to threaten them and has actually thrown rocks and a soda bottle at my youngest daughter. She has cursed children, made obscene gestures toward them and aulted others as she has mine. Myself and other parents have attempted to speak with the child's mother individually and collectively, all to no avail. She told us that we needed to teach our children that her daughter has a disability and that she's not capable of processing things the same way they are. She essentially said that our children need to get over it and just take whatever this child dishes out. This afternoon the mother even threatened a 16 year old in the neighborhood who had told her daughter to shut up and go away (the child was two blocks from home in front of the 16 year old's house taunting her). The other parents and I are at our wits end. We're afraid to say anything to the child for fear of the mother's reaction. Who knows what she'll do if she'll threaten a 16 year old, and we know from experience that talking to the mother is futile. None of us know much of anything about autism, so we're out of ideas as to how to handle the situation. For the moment, I've asked my daughters to push the record on on their cell phones the second she starts (for proof of her behavior), ignore her, keep walking and come in the house and lock the doors when she begins pursuing them. This is really not a solution, as I don't believe my children should be forced to live as prisoners in their home to avoid this out of control child... but it's all I can think of to avoid conflict at the moment. In addition to our concern for our own children, the other parents and I are equally concerned for this little girl. It's only a matter of time before another child snaps and the girl ends up injured. Given these cirstances, what do you guys recommend as the next step for our collective of 10 parents whose children are being hared daily? Do we call the police? Keep trying to work with the mother? What? We're at a complete loss. Thank you in advance for your thoughtful responses.