She will probably have to take out her own subscription, or the two of you will have to take out a Family iCloud+ subscription. Note that taking out a Family subscription will not transfer anything between accounts. It's like having a large room with a movable partition in it. Read this article to learn how to share iCloud+ with your family --> Share iCloud+ with your Family Sharing group - Apple Support
While you can change the email address on your account, it won't change the setup of the account. It will only make it her account to the extent that it will have her email address as the identifier. Note that reusing email addresses can be very complicated. You're really pushing the boundaries of how Apple Accounts are set up and used.
Change your Apple Account primary email address - Apple Support
- If you remove an email address that isn’t an iCloud email address from your Apple Account, it can’t be associated with another Apple Account for 30 days for security reasons. After removing an email address from your account, notify anyone who might contact you on Messages, FaceTime, or other Apple apps using that Apple Account email address. After 30 days, another user might be able to associate that email address with an Apple Account for Messages, FaceTime, and more.
If you can’t change your Apple Account primary email address
- If you try to change your Apple Account to an @icloud.com email address that was created within the last 30 days, you will be asked to try again later.
- If you see a message that the email address you want to use isn’t available or is already in use, check that you or a family member aren’t already using that email address with a different Apple Account. If a family member is using that email address, remove it from their account, then try to use it.
From: How to delete your Apple Account - Apple Support
“Can I use the primary email address for my deleted Apple Account to create a new Apple Account or with another existing Apple Account?
No, once your Apple Account is deleted, you can’t use the email address that you used with it to create a new Apple Account for as long as Apple retains the one-way hash of the email address. For third-party (non-Apple) domain accounts, the one-way hash is deleted after six years. For other accounts, this is retained according to Apple's retention policy, which is reviewed regularly. In addition, you can’t use that email address with another existing Apple Account except as a rescue email. Also, if your primary Apple Account email address is with a Custom Email Domain, it can never be reused to create an Apple Account after your Apple Account is deleted, even if the domain ownership changes.”
