For the past 2 weeks my wife's IMAP account will not log in on apple mail. It was fine up till then. I've lost the password. Is there a way to retrieve it? Or how can I reset it? She still gets email via her POP account but I want to take that offline. It is my understanding that the IMAP account is the way to have email deleted on all devices (IPhone, IPad, and Macbook at the same time. Thanks in advance for any help.
Your account is active as mails are received on pop account,as web mail is configured with mail application .
To reset the password an apple article is there : Change or reset the password of an OS X user account - Apple Support
to take mails offline : Mail (Yosemite): Work offline
You have not told us the email provider. You did attach an article above about the various mail settings you might need from your email provider.
You mention your wife's IMAP account. You also mention her POP account. But you did not tell us if they're even provided by the same provider. If not, then you need your wife's email password to be supplied to you by her IMAP provider.
IMAP Password
