Have the stub for their records, they have the check number and the details. There's a check number attached to the amount she withdrew in her account that they should be able to manipulate/stop. Why do they need the check to cancel it?

I'm sorry, I just don't want these punks to succeed

Edit: I just read about why not. Because these checks are guaranteed funds, the money is immediately removed from the account, there's no delay like personal checks. Basically it's all to maintain the usefulness of the payment method. Criminals would cancel checks and get away with all kinds of purchases without paying if they could cancel these checks.