What checks and balances do you use to make sure all money is accounted for?

We're having a "slight" problem last week our treasurer went to the bank and got change ($240.00) for our event no problem there. It was left in the PTO room and now its gone. We did have a PTO meeting and she came in with it and was sure it was all there and now its missing.
Other question too how do we handle this? Have her repay (there's no way she took it, but she feels responsible) write it off. And do we disclose this to the members.

IMHO I really think someone at the meeting seen her with the bag and took it. It was big bills $5 and $10 to make change and it was just grabbed out of the bag.


HELP

Cindy