We would recommend following the steps here to re-enable set up FaceID both on the device and in the LastPass app: https://support.logmeininc.com/lastpass/help/how-do-i-use-face-id-for-account-recovery-in-the-lastpa...
If that doesn't work and the option still isn't there, please try uninstalling the LastPass app, restarting the device, then re-enabling FaceID in the LastPass app following the steps above.
Thanks, it's working again!
I think that restarting the phone was critical, when my wife just reinstalled the app, that didn't work.
When she restarted, it also prompted her to do a software update, so I can't be certain that that had nothing to do with it (she had other problems from an earlier software update as well), but FaceId is working for LastPass again.