One of my employees submitted her prior period timesheet late, and now she cannot track her time for the rest of the week.

Thanks for reaching out to the Community space, @lindasuewaldron.

Let's unlock your employee's timesheets so they can start tracking time again in QuickBooks Time.

You can use the Unlock Exported Time tool to unlock your employee's timesheet. To do this, you'll have to make sure you're an administrator, group manager, or team member that has the Manage my timesheets permission.

In addition to that, please note that you can only unlock time up to 90 days in the past.

To unlock time, here's what you'll need to do:

1. In QuickBooks Time, go to the QuickBooks dropdown and select Unlock Exported Time.
2. Choose a Start Date and an End Date.
3. Click on All employees and choose individuals, groups of employees, or all employees to unlock time for.
4. The timesheets that will be unlocked are displayed for reference. Hit Unlock Timesheets.
5. In the notice that displays, select Confirm unlock.
6. Go to Approvals and choose the same date range and employees you chose to unlock.
7. Click on Unapprove for each employee.
8. In the Approvals Report, Time Entries > Timesheets, or anywhere you can edit time, make your desired changes. 
9. Go to Approvals and re-approve the timesheets.

You can read this article for the complete guide: Unlock QuickBooks Time timesheets exported to QuickBooks.

Also, you may want to check out this article as your reference to guide you in managing employees' timesheets in QuickBooks Time: Approve, unapprove, and reject timesheets in QuickBooks Time.