I wouldn't have paid her a dime. She brought that money in and your friend doesn't even know how much money was truly in there to begin with.
All sounds a little shady to me. I was VP of a PTA for my sons school in 3rd grade and we never left the money with one person before it was counted. We all did everything together and made sure that no one person was left holding the bag when it came to the money. There was always at least two of us together doing sales and such and the money was always counted by two people immidiately after each event, even down to the lolipop sales on Fridays. When deposits were made, it was made by 1 person, but the deposit slip was made out by two. The money was counted, deposit slip filled out and then it was counted by the second person and verified, and then and only then did just one person take the money to the bank.
That was to cover everyone should there ever be any question about any of it.