Drag slider on left hand side to show folders.
Use the "All Folders" view rather than "Smart Folders". You can click the left and right arrows at the top of the Folders column on the left-hand side to switch Folder views. "All Folders" is the traditional view. You can also go to the View menu, select Folders and choose the folder view you'd like to see in Thunderbird.
Customize your toolbar to add the icon to the toolbar and reset the toolbar to default. (Right-click any grey space at the top of the Thunderbird window, select Customize... and choose from there.)
Check the Google App Status dashboard first to check if there's a known issue with Google mail. If not, have the user unsubscribe from the All Mail folder, which can take up a lot of memory. (Have them right-click on the e-mail account on Thunderbird, i.e. firstname.lastname@example.org in the left-hand column, then select Subscribe. Select the [Gmail] folder, then click on All Mail and click Unsubscribe.) You can also have them try rebuilding the index by right-clicking on a folder, selecting Properties, then choosing Rebuild Index. If the problem persists over a period of time, we'll need to get their server address and report it to Google.