ios 15.8.2 imessage not working

Hi,

I re started an old iPhone 7, software 15.8.2, I have signed into my 10 year old daughters iCloud account and her iMessage is still not working or linked,

I have done all the usual stuff, signed out and back into her account, tabled off and on messages in her account and still all my old iMessages are still there.

Also a lot of my old photos are still there even though I am not signed into the phone, any tips on how to get her iMessages onto this new phone for her? thanks