Hmm-you could take her out back and beat her with a rubber hose, or maybe put the stun gun to use?
I'm assuming this is only with events she's chairing, or somehow in charge of (that is, other people who run an event haven't been instructed to give money to her). I could think of a couple of reasons WHY she's doing it, expecially if she DOES eventually hand the money in, but HOW to handle it is another story.
I'm sort of with melloweer--making a new policy from this point forward that the only people to handle money are the committee/fundraising chair, president and treasurer on one hand makes sense. But then that could get weird if she HAS to chair an event, or if she's part of an event where money has to be collected (like a catalog sale), or you have other people collecting money (like with a cash register/box). It's going to happen--the fundraising/committee chair can't always be the only ones taking money, be it collections from catalog sales or running the drawer at the book fair.
Definitely make a rule that ALL proceeds from any "event" MUST be given in to the President, Fundraising Chair or Treasurer AT THE END OF THE EVENT. Everyone meets at a designated time/place to give up the money. That way, she doesn't get a chance to get it home. If she DOES "sneak" it home, go to her house the next day, unannounced. Nothing accusatory, nothing suggested, you were in the neighborhood and figured you'd take it off her hands. As uncomfortable as confrontations can be, in the end you have to think about yourself, and the repurcussions this kind of thing could have on you, your family and the membership as a whole.
What a bummer--why can't everyone be normal, like us

?