I'm always a bit bemused by the "Is this really her/him?" statements. Clearly, right now, yes, it is her, because she's doing it. No duress.
But what she's doing, however reprehensible (and yes, I think it is), doesn't entirely define Who She Is, any more than any failure attributable to you over the years entirely defines Who You Are.
It seems like that question wants to address Why? more than Who. Is she doing it out of spite, weakness, a total surrender to selfishness, a sense of imprisonment, overweening entitlement, vengeance, a desperate bid to feel attractive as she ages, well-nigh physical dependence on the high? What motivation can you live with, if any?
Really, the only question you can answer is, given that this behavior is clearly a *facet* of Who She Is right now, am I willing to endure it in hopes that it passes, and if so, for how long?
FWIW, I don't think your anger is misplaced. Even if you take the ego out of it.... emotionally, she is feeding your family's food to a stranger. I don't know many people, male or female, who would take kindly to that.
No good answers on tactical.... sorry.
"Show me a completely smooth operation and I'll show you someone who's covering mistakes. Real boats rock." -- Frank Herbert