On iPhone 15 now running iOS 26, lost ability to send messages to Android user (cellphone) on their iPad (with their Apple ID). How do I fix this?

My sister has an Android phone and an iPad. Suddenly she's not able to receive texts or images from me in Messages on her iPad. I've spent the last 2 days--updating to iOS 26 then working with AI to try to resolve the issue. I've deleted and added her back as a contact, rebooted a number of times, changed my default sending ID from my cellphone to my apple email. I needed to delete all conversations where she was a part, but despite reactivating threads, reconnecting her continue to find "ghost" conversations:

"We have now ruled out:

• Spotlight indexing
• Siri suggestions
• Normal Messages deletions
• iCloud sync mismatches
• Cached contact identities
• Hidden “group contact cards”
• Stuck indexing after reboot
• Missing Spotlight/Siri menus in iOS 26
• Insufficient storage
• Messages-in-iCloud disabled/enabled cycles

And everything you have described points to a very specific problem:

🎯 The “ghost threads” you see are Message database orphan entries

This means the SQLite Messages database on your device still contains message thread metadata, even though:

• the conversation is deleted
• the contact card is deleted
• Siri/Spotlight indexing is disabled
• your phone rebooted
• Messages in iCloud was toggled

These “stub” threads:

• appear only in Search
• open as a blank screen
• show participants at top
• cannot be deleted
• cannot be left
• do not allow typing
• show “Add to Contacts”
• persist even after iCloud cleanup
• do NOT appear in the list of conversations
• still appear even after “Sync Now” or reboots

This is classic orphan-thread behavior and is known in the developer community as:

Chat.db orphaned handles / orphaned chat entries

And in iOS 26, because Apple changed the structure of Messages + Siri, Spotlight can no longer purge these on its own."

So what do I do now?