What about syncing iPad to iPhone?

Hi geniuses!

so my wife is going nuts because her iPad and iPhone don’t sync her Messages. I’ve tried doing all suggested online - making sure she’s signed into her iCloud account on both devices, etc. But it doesn’t work. Sometimes she’ll get an iMessage on her phone but not on her iPad. Sometimes only on her iPad and not her iPhone.

Any ideas for something I could try to bring harmony to our house once again??

Thanks!