there are a couple of 'simple' ways to send emails securely. one doesn't involve 'sending' at all.
just open up a webmail account, let's say at yahoo.com, and leave messages in your account's notepad, or draft, then give your girlfriend access to your account. this way, 'emails' are never actually sent.
if you insist an actually 'sending', then each of you can set up a pgp account at hushmail.com.