Did you see her do these things? I’d file a police report and remove your son from the home immediately. If it’s your home, tell your DH when his DD has visitation she is not to come to the home & he’ll have to see her elsewhere. The safety of your child is your top priority, and if she’s resorting to violence you need to take a zero tolerance attitude. 

Either she stays out of the house or you get your own place. 

The only thing to do is call the police. You need to get out of the house until she is removed.

Does your DH have custody? Where is her mother? What is that relationship like? Can you tell her mother what happened and tell her to get her child immediatly? What does your DH say??

Press charges.

Call the police immediately. If your SD actually did this she needs help and you and others need to be protected from her. If she didn't, an investigation might turn up who did.  This is serious stuff.

Unless and until it's determined that SD had nothing to do with it, no SD in the house or near your stuff.  If it's your DH's house and he refuses to keep SD away, leave him.

SD coming back into your home shouldn't even be an option. I'd make a report on this and have your H seek professional help for her because obviously she's not all up there. When your health and that of your family, safety, and well being are in jeopardy....all bets are off. This girl needs to GO!!!

"How old is SD?" 

"Doncha know she's been through HELL as a child of divorce/separated parents; cut her some SLACK?"

"Maybe she was just kidding?"

"It could have been an accident.  There's not a DAY that goes by when I think I may one day confuse the toilet cleaner with toothpaste."

"You should be ashamed of yourself for DARING to be in precious SD's life, you homewrecker you!"

"Has her father suggested counseling followed by ice cream sundaes at the local ice cream joint?"

Radio silence by non-SMs  on this site.

Leave now with your son. Both of your safety is the most important thing.  If you choose to stay in this dangerous situation with your child he could be taken away from you. 

File a police report and go. Be prepared for the fact that SD may lie, deny and say you framed her.  I hope that she will be removed from your home and get help but if she and her father fight it it likely won't happen.  

Please don't become another news story.