Hi Leigh Cook.
Ads in Outlook for Android usually show when the app isn’t linked to the Microsoft 365 Family subscription. Being signed in with the BT (IMAP) mailbox doesn’t count for the ad-free benefit.
Fix: In Outlook on Android go to Profile icon > Settings > Accounts > Add account > Add Subscription. When it asks you to sign in, use the Microsoft account she used to accept your Family invite (it might be the same BT email address, but she must choose/sign in as a Microsoft account, not add it as IMAP/BT).
Once the subscription account is added, the ads should stop.
For reference: Ads in Outlook Mobile
Please let me know if this proves useful to you, or if you would like further assistance.
I'm looking forward to your reply.
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