Managing subscriptions on child's account

Hi all.  I really hope that someone can help me.  My daughter (12) has an iPhone and I don’t.  Her Apple account is linked to my email address.  I got an email this morning saying that she’d purchased an app (although she swears blind she didn’t).  I only had today to cancel it as it was a trial followed by monthly payments.

Anyway, here’s my issue.  She went off to school with her phone and I wanted to unsubscribe.  It took me an hour and a half and in the end I had to contact Apple to get them to do it. When I clicked on the ‘review your subscription’ link on the email, it took review the subscription. me to an iTunes link which wouldn’t open and it told me to open up the iTunes app on my PC. I did that but that’s just my Apple account and not hers so I couldn’t review the subscription.  I’m told that even with Family Sharing, I can’t add her account to mine.  So the only way that I can view/manage her subscriptions seems to be through her iPhone. Is that right?  I really hope there’s a way I can do it online/from my PC. 

Can anybody advise please?

Thanks in advance.