On the Apple Family iCloud backup storage plan, why doesn’t my wife’s nightly backup get stored on our 200 Gig Family Storage Plan?

I subscribe to the Family Plan iCloud Storage, and included my wife on the plan, to share the 200 Gig.backup capacity in the cloud.

My phone’s backup goes into that 200Gig plan just fine, but my wife’s phone gives her messages that her 5 Gig capacity is now exceeded, and her phone will no longer back up unless she buys more iCloud backup capacity from Apple.

I thought on the Family Plan, her phone would back up automatically into the 200 Gig Family Plan.

What can I do to get her backups into the 200 Gig backup bucket so she will not have to buy extra capacity. Our family plan bucket has plenty of excess capacity.?

Jimdpi