So it works on windows? If so, then it's probably not a hardware issue.
What I could recommend to help track down the issue:
test another distro, if possible - sitting here on NixOS it works for me
test another display manager (aka X11)
test another desktop (KDE, LXDE, whatever)
If it's none of the above, you might need to get your hands dirty
check if it's always the same monitor
check the logs (journalctl --boot -xe) maybe something will jump out
monitor the reconnection of peripherials with sudo udevadm monitor
start it when everything's booted up and everything's plugged in
disconnect problem monitor then reconnect it and observe the output
suspend then wake the computer and check the output
That might give you a hint of what's going on.
There's a change something isn't working in terms of drivers. You can probe her computer with the executable from https://linux-hardware.org/ and share uploaded result here. Maybe there'll be an indication of a missing driver or something.