Apple One Family Sharing to someone with two Apple IDs

I'm planning to add my daughter to our Apple One subscription via Family Sharing, but she has two Apple IDs (one for iCloud and one for media/purchases/subscriptions). It's not clear to me which of her two Apple IDs I should add to our family group. I want her to be able to piggy back on our iCloud storage (she's currently paying for her own with her iCloud Apple ID) and also be able to take advantage of our Apple Music/Arcade etc. services. Wondering which of her two Apple IDs the invitation should be sent to to give her the most trouble-free experience when joining the family. She already has lots of purchases under her media Apple ID. I actually asked an Apple rep this question but so far they haven't quite understood what I was asking.