My wife uses her computer only rarely. Every time she tries to sign on, her password has expired. I know there's a way to keep the password from expiring until I (administrator) tell it to. I'm darned if I remember how to do it and looking through "users and passwords" doesn't show me ... how?

"net accounts" is the cmd you are looking for.. you run it in a cmd window. It is one of the net services commands, and help is here...
Paste this into a run window: %windir%\hh.exe ms-its:%windir%\Help\ntcmds.chm::/ntcmds.htm
or on the net here:
Of course, that method treats your wife as an equal.. that may not suit your religion, or you may just wish to keep that little bit of extra control over her... so in that case use "net user"
Help is in pretty much the same places.