Sean, you can verify this information. Take her earnings statement for the period prior to the vest, the period of the vest, and the period after the vest, and you should see the numbers for the tax buckets change; depending on the detail in her earnings statement, you will see differences in the Federal, Federal Supplemental, Medicare, Social security (unless she's maxed out), State, and SDI if you have that. Or you can go to your finance department, ask the admin to point you to the person responsible for RSUs, and that person can run the report for each vesting in about 10 seconds or less. But I don't think you need to worry about that; taxes get paid or people go to jail.
