I knew someone like this and it really, really sucks. Just like you, it goes hand in hand with other addictions like cigs and gambling.
It really, really sucks because if you like me and you live somewhere where it's legal and you love weed and you can smoking it for decades, it can be really hard to single out someone with a problem because everyone used to weed being so relatively harmless.
What I can tell you is there is no sense here, 15 Js a day of proper, quality dispo weed is beyond reason. It was the same for me with her, she'd finish one and just light the next up like they were Marlboros, I have no idea if she was even enjoying getting high because it didn't seem it.
You have to put your foot down and set a hard line. You have kids here and you have to step in and do the right thing. Unless you're bonkers loaded, you're not going to be able to spend 1,600 a month on weed for her. And your option to grow it yourself might seem good in theory but she's just going to use her elephant tolerance to blow through it, you as a novice grower are not gonna feed her appetite.
I can't tell you about how anyone person is going to act or react. But what I can tell you is when you're dealing with this sort of person they're going to get what they want regardless. Be prepared when you cut it off, if she has access to your money she may do drastic things, if she doesn't she may very well find herself spending time with anyone who has it.
When I can tell you is it isn't very hard for a woman to find free weed. Sorry. Silver lining here, no one's going to put up with her habit for more than a few days or weeks either.
I'm truly sorry.