You said that her debt and money problems are self inflicted. Therefore, the underlying problem is likely due to either drug addiction, gambling addiction or compulsive shopping (also addictive behavior).
She is clearly out of control as evidenced by her totally unjustifiable stealing from family members. As you’ve discovered, your toleration of this behavior is merely enabling her and not helping the situation at all.
I strongly urge you to follow the advice of Lucky Guy regarding changing accounts, passwords and whatever else you need to do to protect the business. Since you’re the majority owner, you don’t need anyone else’s permission or agreement to do this.
It is YOUR fiduciary responsibility to protect the business from any further money drain. And you MUST do this PRIOR TO any discussion of this with either her or other family members.
Your parents, although well-intentioned, may immediately get on the phone with her to try to resolve things. You must have the business accounts protected from any further embezzling.
And, yes, that’s a dirty word but it is what it is, family member or not and carries legal penalties with it. You need to start being rigorously honest in your language to yourself so you don’t keep tolerating it.
Once the business assets are protected then you have the time to begin problem solving on the most compassionate and helpful way to deal with the roots of the problem (which might possibly involve a long term treatment center.)
For someone to act as your sister has done, there HAS TO BE some very deep dark addiction-type issues underlying it all. People don’t just betray family members on a frivolous whim.there is something underneath it all and hopefully she will be relieved to being forced to bring things into the light and begin to deal in honesty. She certainly can’t be feeling very good about herself and the dysfunctional decisions she’s made.
Yes, she does need professional help buy prior to that, you NEED TO PROTECT the assets of the family business.
Welcome to Fluther and hopefully you’ll find help from many of the people chiming in on this Q. It’s a serious situation you face but at least you’re now ready to put a stop to it rather than allowing it to continue out of misguided love for your poor sister who is clearly in over her head.
And, you either need to hire a competent bookkeeper or have you or another family member take that position. That’s down the road apiece but at least you can start considering possible candidates now.