Hi there!
Good step in creating different Apple IDs!
If her iMac currently has your Apple ID signed in, you'll need to sign out of your account, create a new Apple ID, then setup Family Sharing. Before you begin, taking a look at this article may be helpful: Make sure that each family member has a unique Apple ID - Apple Support.
To begin, sign out of iCloud on her Mac: Sign out of iCloud on your iPhone, iPad, iPod touch, Apple TV, or Mac - Apple Support.
1. Choose Apple menu > System Settings.
2. Click your name.
3. Click Sign Out, and follow the onscreen steps.
4. If you want to a keep a copy of your iCloud data on your Mac before you sign out, make sure that you select the appropriate checkboxes. Then click Keep a Copy. This might be a useful step to download the iCloud data you'd like to upload later to new her iCloud account by saving it to the Mac first.
Next, after you're signed out of your Apple ID, create a new Apple ID on her Mac: How to create a new Apple ID - Apple Support.
1. Choose Apple menu > System Settings.
2. Click Sign In with your Apple ID from the sidebar. In earlier versions of macOS, click Sign In.
3. Click Create Apple ID, then follow the onscreen steps to provide an email address, create a strong password, and set your device region. The email address that you provide will be your new Apple ID
4. Enter your credit card and billing information, then click Continue. You can also choose None. You won't be charged until you make a purchase.
5. Check your email for a verification email from Apple and verify your email address.
After you verify your email address, you can use your new Apple ID to sign in to the App Store and other Apple services such as iCloud.
Finally, you can setup Family Sharing: Set up Family Sharing - Apple Support. If you haven't already done so, one adult in the family — the family organizer — needs to set up Family Sharing for the group from their iPhone, iPad, iPod touch, or Mac. After the Family Sharing group is setup, you can invite the other person to join.
Hope this helps! If you have any questions, let us know!
- Jack
