When you delete a donation in GiftWorks that you have already posted to QuickBooks, QuickBooks does not automatically update your posted information. GiftWorks handles a deleted donation by producing a new transaction that reverses the original transaction.
In order to update your QuickBooks file, you must post this reversing transaction to QuickBooks.
You won't need to do a special posting as GiftWorks will include the reversing transaction in any standard posting that is picking up its date. However, you do need to post this correcting entry before you permanently delete the donation.