To provide only Adele Vance with the ability to turn on and off Teams preview features, you need to create and assign a custom update policy for her. Here are the steps to do so:

Sign in to the Microsoft Teams admin center with your Microsoft 365 username and password1.

In the left navigation, go to Teams > Teams Update policies.

Select Add to create a new policy or select an existing policy to open Update policy.

Name the update policy, add a description, and select Enabled from the drop-down menu for Allow public preview. This option enables Teams Public Preview regardless of whether a user is enrolled in Office Current Channel (Preview). The end user must also opt in to Teams public preview in their Teams app2.

Click Save and then Close.

In the left navigation, go to Users and then search for Adele Vance from the list of users.

In the user details page, go to Policies and then click Edit next to Assigned policies.

In the Assigned policies pane, under Update policy, select the policy that you created or modified in step 4 from the drop-down menu.

Click Apply and then Close.

Now, Adele Vance can turn on and off Teams preview features by following these steps in her Teams app3:

Select the three dots to the left of your profile to display the Teams menu.

Select About > Public preview.

Select Switch to Public preview or Switch back to standard version.