Q: my child's ipad will not send request to buy to my iphone.  she has her own apple id

Try these support articles:

Get help using Ask to Buy in the iTunes Store - Apple Support

Request and make purchases with Ask to Buy - Apple Support

If that doesn't help you can also call or chat with Apple Support: Contact Apple Support

-AJ

I had the same issue with my son. I created his account before Family Sharing so I entered an older birthdate. (I know, tsk, tsk), I fixed it by changing Apple ID to a "Child" account.

Log into iCloud on your computer and check in Settings > Family Sharing. Be certain your daughter's account is a child account. It will list her age rather than say "Adult". If it says adult, you will need to modify her account details. Usually, this is because you entered a wrong birthdate. If this is the case, log into iCloud with her Apple ID and pass. Change the birthdate and you will be prompted with instructions. You will be sent an email confirming the change.