Hi Mark Zelakowski,
Thank you for posting! From our understanding, you are getting an error message that your daughter doesn't meet the age requirement to enable Apple Cash on her device but you are also unable to enable it through Family Sharing because it says it is already enabled, is that right. The age requirement is 18 years old so the error on her device is expected behavior. Let's work on getting Apple Cash Family set up. Are you the Family organizer? Are all of the device up to date running the latest iOS? Have they been restarted since noticing this issue?
Restart your iPhone
You should also confirm that the regions for all devices is set to the US when you go to Settings > General >Language & Region. Check out this article: Set up and use Apple Cash Family.
If you are still unable to set it up, you should reach out to Apple Support for further assistance. You can reach them here: Get Support.
Hope that helps!