I presume you each have separate accounts?
You are correct, she should not need approval. Is it possible she has her account set to a child age and you have Ask To Buy set on the account? If that is not the reason (and I think it is very remote) then contact Apple:
Refer to this page for Apple Support features ➔ Contact - Official Apple Support
Select from the presented options until you find a solution for your issue, or see if there is a chat or phone call contact method offered lower on the page under “Get more help” (you sometimes have to narrow down the options multiple times before this is shown). If you do not see your issue, keep experimenting with any series of selections until you reach one that offers a chat session or a telephone call and get the representative to redirect you. For chat, you can also try using the Apple Support App —> https://apps.apple.com/app/apple-support/id1130498044
This support article has various country telephone numbers for contacting Apple for support and service ➔ Contact Apple Support - Apple Support For some countries look under “Other” listing at the end of the list. Not every country has telephone support, and phone numbers may only work when calling from the same country.
For chat help with a USA Apple Account —>
https://getsupport.apple.com/?caller=kbase&PGF=PGF63005&category_id=SC0998&symptom_id=20198