I started out with an IPAD and Apple account. As time went on I purchased an Apple Iphone for my spouse. When I installed her Iphone, I used my account to set it up. I am getting her an Iphone 13 for Christmas. I want to separate the accounts.

You can transfer her data from the old phone to the new phone using the steps in the articles below.

Transfer content from an iPhone, iPad, or iPod touch to a new device.    *

 Quick Start to transfer data from your previous iOS device to your new iPhone, iPad, or iPod touch.  *

 Use iCloud to transfer data from your previous iOS device to your new iPhone, iPad, or iPod touch   *

Set up your iPhone, iPad, or iPod touch - Apple Support.   *

https://www.youtube.com/watch?v=3rHtV3ZDdgQ&list=PLIl2EzNYri0fwwkKJtNNX2CksbIqfUuql&index=2

Then change the Apple ID. When changing to the new ID, there may be some data loss, but you can minimize it. If syncing photos with iCloud, ensure Optimization is turned off in Settings/Your Name/iCloud/Photos and/or in Photos/Preferences/iCloud. Then make sure full resolution photos are on the device/computer. When signing out of iCloud, if asked whether you want to retain data, choose yes. Messages conversations will be lost if they are addressed to the ID. See the article below for other places that the old ID should be removed. See Winston Churchill's response in the below discussion.

 How to switch Apple IDs on your iPhone or iPad.      

How to transfer all files from one iCloud account to another.       

What to do after you change your Apple ID or password - Apple Support.      

If she doesn't have her own Apple ID, she'll need to create one at appleid.apple.com.

Everything currently on the device is tied to your Apple account so it will not transfer to her account. But, you can set up a family share to share purchases. https://www.apple.com/family-sharing/