iCloud error connecting on MacBook

Hi there. I'm really struggling with this one and none of the ideas I've read online are working.

The MacBook is continually receiving the error connecting to iCloud message. I've tried...

Quitting all apps using icloud.

Used activity monitor to close processes using icloud.

Removed icloud configuration files.

Tried to log out of iCloud - can't.

Booted mac in safe mode and still nothing works.

Changed iCloud password via safari.

Disconnected from Wifi to try above options.

Need to connect to icloud to correct the problem, but not possible.

None of the icloud options are checked on the iCloud preferences screen and toggling them makes no difference.

Initially my wife and I shared an account ID, but about a year ago when she got this MacBook, she created her own id and is on family sharing. Never had any problems with iCloud until now. Her account is working fine on her iPhone, even with the password change which was accepted, but the MacBook icloud is just not accepting anything. It will routinely look as if it is signing in and then just stop. Next time, it will say that password is wrong. Then it will send a verification code to her phone, then say password is incorrect. It isn't and then it directs to a message about iforgot and will receive details on how to unlock account within 24 hours. That's happened twice with still no reply from iForgot regarding this (Phone calls, texts, emails..checked in junk, trash spam etc). However, I can still sign into the app via safari web page and her phone. What gives?

Other than a reinstall I'm struggling to see a way out of this I haven't tried...and even then I'm not sure that'll work. I apologise if I've left out any other things I've tried when writing this. Mac is up to date with latest High Sierra.