I have an apple family music subscription and my wife cannot have access

Welcome to Apple Support Community!

I would start with this resource below to resolve your issue

If you don't see your family's shared content : https://support.apple.com/en-us/HT201454

If that doesn't work, I would have the organizer check the Apple ID they are using for purchases.

This is how the organizer can check:

1. Settings
2. Name
3. Family sharing
4. Tap on their name at the top
5. Tap Account
6. And you should see the Apple ID that is being used for Media and purchases (subscriptions...etc)

If that Apple ID in media and purchases is not the same Apple ID that has the Apple Music subscription, she will not have access. You will need to change that Apple ID to the correct one.

Hope this helps ;)