Can I recover someone's WhatsApp chat history after I've mistakenly changed phone numbers?

I've got all someone's chat history on my WhatsApp number after trying to help her when her phone broke. I want to get it back onto her WhatsApp number - can anyone help? When her phone broke, I tried to help out by lending her my phone. I used WhatsApp's Change Number feature to change from my number to hers. Then when I got her a new phone, I used Change Number to go back to my number. But I didn't realise Change Number changes the number in all Chats and Groups. All her chats and groups now have my number in them. So now I get my messages, plus any from her Chats and Groups and I have her entire history on my number. Can anyone see a way to untangle this mess? I'm in a lot of trouble. Things I have tried: - She has set up WhatsApp on her new phone with her original number but the history is gone. - I've looked at restoring an old version of her WhatsApp backup - but I think her history has been over-written by recent backups after this mess happened. I can't find any previous versions on Google Drive. - I looked at transferring my backup to her, but don't think this is possible. - I said I could email her individual chat histories - she wasn't impressed. Any ideas are welcome. Both our phones are Android.