My 18 yo step daughter is a heroin addict. She just completed her second detox program and less than a week later is using again and lost her job as a result of it. I am just waiting for the stealing to start up now that her money source is about to dry up. She has stolen smaller items like jewelry from her mother and sisters, never anything from my home. Nothing was ever done about it and to this day, she feels no remorse over it.
There is a lot at stake here and babying your niece is doing no one any good, especially her. She has to have consequences in order to want to make a change. No consequences leaves her with no REASON to want to change. The drug has it's hold, the high is what they crave and as an addict, they will never NOT want the high so they need other reasons to want to quit.
If your niece had stolen $150 worth of belongings, I would say pressing charges would be a bit harsh but $15,000 is a no brainer for me. I don't believe an active addict would feel bad about having done this, her focus is on getting money to get her high. nothing else. Filing charges, as hard as it will be, *may* be her saving grace, only time will tell but at least you did something.
My husband sometimes has a difficult time holding his AD accountable and following through on consequences. His ex-wife is a complete enabler, I can't talk any sense into her but I can with my husband. When he has a difficult decision to make, I ask him this.
If she overdoses again (our AD has twice) and she doesn't live through it, can YOU live with the fact that you did nothing when you had a chance to do something? I think the guilt would eat him alive. Doing nothing is worse than making her accountable for her actions. It is in my opinion, anyway.
You need to talk frankly with her mother, this is not the time to ***** foot around difficult conversations. It has to happen.
Good luck to you!