I agree with the idea of wasting $2 for every $1 she puts into the Worldwide Pedophile Defense Fund without your permission. She puts in $1, you waste $2 worth of littera-trash. She puts in $10, you waste $20 worth. And so on. It doesn't have to be littera-trash: If you can waste their money by running up their bills, that counts. And, leaving the lights on in the Kingdumb Hell all night ought to run up a pretty big light bill; so will setting the air conditioner at 55 F and leaving it there all night (with a window open, to waste even more of their money). A note that this happens to waste double the amount she puts in the box ought to put a stop to it.
Another suggestion is to donate equally to an apostate cause per dollar that gets put into that box. You could donate to one of these forums, to Freeminds, Silentlambs, or to help Cynthia Franz go through this hardship. Every dollar she puts into the box is matched with one put into an apostate site.
Yet another, and one that would waste even more of their money, would be to stop payment on the check. This works best if the check is around $35 or bigger--it will probably end up costing you something in the order of $20 or more per check you do this with, but it will cost them money at the other end. I think these "without your permission" donations will stop if each one results in, not a $35 gain but a $30 loss to the congregation. I assume you are the boss, since they even claim from their own doctrine that the husband is the head of the household.
Either way, this is a complete waste of your resources. Every penny that ends up in one of those boxes is money that is being thrown away. She is probably brainwashed enough that the promise of a new material treat with the money saved from not donating to the Kingdumb Hell will not work. If you control the account, I strongly suggest that you lay down the law that no more of your money be diverted into this complete waste, since you did not agree to portions of it being thrown away. If she is earning the money separately, unfortunately it would be hers to throw away; still, a matching donation to an apostate cause or a matching waste of congregation funds would deter continuation of this waste.