https://support.mozilla.org/en-US/kb/calendar-updates-issues-thunderbird

The calendar updates issues link is where I started. And as I stated, the reset procedure given did not work. There is nothing else in the link that appears applicable.

the reset procedure given did not work.

Please explain in detail what you did, and what happened.

I followed the procedure given in the first part of your link under the heading "Lightning disappears after a Thunderbird update (release and beta versions)". I tried the 6 steps a total of 3 times being careful to do it exactly as written, but found that Lightning never showed up in the extensions list. To be sure I was looking in the correct location I went to the same place on my wife's computer (also a Windows 7 PC with the TB 60.3.2 update). Lightning was in the extensions list there. So I tried uninstalling Thunderbird on my computer, downloading it, and reinstalling it. Still no Lightning. I retried the 6 step procedure above with no success. I looked for the option of downloading just Lightning, but that's no longer available.

Open the profile folder. https://support.mozilla.org/en-US/kb/profiles-where-thunderbird-stores-user-data#w_how-to-find-your-profile

In the profile folder is a subfolder 'extensions'. In 'extensions', do you see a subfolder '{e2fda1a4-762b-4020-b5ad-a41df1933103}'?

If so, delete it while Thunderbird is closed. Then run through the 6 step procedure again.

The extensions subfolder is empty.

I don't know what else to suggest other than creating a new profile using profile manager. https://support.mozilla.org/kb/using-multiple-profiles

Then start Thunderbird with the new profile.

Is Lightning visible in the Add-ons Manager window?

I created a new profile. The calendar does show up with that profile, but Lightning is still nowhere to be found with my default profile. What's the best way to get a profile with my data that includes the calendar?

I don't know what's wrong with your existing profile. Therefore the suggestion would be to set up your calendar and email accounts in the new profile. You can also manually migrate data from the old profile. http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Thunderbird

Also make sure to create backups for both, the old, and the new profile. https://support.mozilla.org/kb/profiles-where-thunderbird-stores-user-data#w_backing-up-a-profile

I was able to bypass the problem and get the calendar back by following your suggestion to create a new profile and move my data. Seemed a bit draconian, but it worked. I really appreciate your support to find a resolution. Merry Christmas!

Good. For future updates, this should just work, without the need for manual action. When your problem is fixed, can you mark the topic as 'Solved' please? Thank you and Merry Christmas.