I've sent an iTunes Gift to an email address that no longer exists

Click on this link to find out how to 'Resend iTunes Gifts' --> Gift apps, music, movies, and more from Apple - Apple Support - "If you sent an iTunes Gift and your recipient can't find the link to redeem it, you can resend them the gift from your iPhone, iPad, or iPod touch or your computer. When you resend an iTunes Gift, the recipient will receive another email with a link to redeem the gift."

but I have sent it to her old email that no longer exists how do I get it back

Cancel a gift

If you want to cancel a gift, you can contact Apple Support up to two days before scheduled delivery.