In quickbooks, make sure the "audit trail" button is turned on so you can see changes made to original transactions (you can find this under company preferences). Quickbooks does not automatically have this checkmarked and you have to do it manually. The exception is if you use the online version of quickbooks, which does automatically turn on and use the audit feature.
This is a basic internal control for any medical practice using quickbooks. It allows you to see for example a check written to a person and then changed to a name of a common vendor to conceal the theft.