This is awful!
I don't understand why the Dad feels he might have to go somewhere, it's the addict who needs to go to rehab. He should discuss that with her or tell her that he's calling child protective services.
It is traumatizing to that young child to see that and only a matter of time before she tells someone at school who will call CPS (they are mandated reporters) by telling you she is crying out for help.
I hope that you are able to get some help for all involved and absolutely everyone here will be in full support of you.
Best of luck,
Jules