Hi balernograinger,
We understand that you have some questions about iCloud storage plans and we'd like to help. To clarify, each Apple ID includes 5 GB of free storage space, and you can upgrade to plans of 50 GB, 200 GB or 2 TB.
When you upgraded the storage plan for your wife's iPhone, was that done from your Apple ID account or another one? The reason we ask is that the increased storage will be associated with the Apple ID account that was signed in when it was purchased, and the subscription will need to be removed from that account. We have more details here:
Manage your iCloud storage
If you're also using Family Sharing, the group members also have the option to purchase a larger storage plan to share.
Share an iCloud storage plan with your family
Please let us know what you find, and we'll take it from there!
All the best.