If you both use the same e-mail address you can't both use OE in your separate user accounts. If you do, you'll find that sometimes e-mails are downloaded to OE in your wife's account and at other times you will download e-mails to OE in your account.
The are 2 solutions:
You must agree that you will only download e-mails into OE in one account or the other.
You should each have a separate e-mail address and you can then use OE in your own accounts for your own separate addresses.