How to collaborativly share iCloud storage with overloading the storage?

The shared photos shouldn't count against her storage. See the following from How to use iCloud Shared Photo Library - Apple Support

All participants have equal permissions to add, edit, and delete content in the Shared Library, while the person who set up the Shared Library, the library creator, provides iCloud storage for all of the content. Everyone else gets access to the Shared Library content without it counting towards their iCloud storage.

You may want to review what is in her iCloud storage to see everything that is currently there. See information in Manage your iCloud storage - Apple Support

Also note that you can share your iCloud storage plan. Doing that doesn't share the data (like iCloud Shared Photo Library does). It just makes your storage plan available to everyone in your Family Sharing. Each person's data stays separate and private. See information in Share iCloud+ with your family - Apple Support

Did you share the storage as described below from Share iCloud+ with your family - Apple Support

On your iPhone, iPad, or iPod touch

In iOS 16 or iPadOS 16 or later:

1. If you haven't set up Family Sharing yet, set up Family Sharing. 
2. Go to Settings > Family. 
3. Tap Subscriptions.
4. Tap iCloud+.
5. Follow the steps to share your existing plan.
6. Use Messages to let any family members with an existing iCloud+ plan know that they can now switch to your shared iCloud+ plan.

You have to initiate the process by going to System Settings > Family > Add member