I've performed a Malwarebytes scan and a Windows offline scan, but nothing shows up in the Windows scan history.
For instance a number of years ago Thinkpads added a UEFI setting which can be set to disable the ability of Windows to update firmware.
Then I would want to consider what kind of gf she is.
These have been around a lot longer than laptops but the tendency of some to function primarily as an "evil maid" is still as prevalent as ever.
In that case the laptop is the least of your worries.
Go to the manufacturer of your laptops website and go to the support page and check to see the model number and find the latest BIOS and driver updates and cross-reference that with the date that you find in the BIOS.
It could have been a full-blown bios update. If it's an Intel chip it could be a management engine update.
Now you do say "My laptop". I do need further clarification here. Does that mean it's yours as in you bought it for home and personal use. Was it provided by work and you didn't buy it and it was requisitioned to you by IT? Because there are many factors here that could be at play.
You worry that she's subverted the system, intentionally or otherwise?
You're concerned that she didn't update windows?
If you trusted her with unsupervised access to the hardware, theres some possibility she might "do something" do it. If you can't live with that thought, lock up the hardware when its not in your hands.
EDIT: perhaps a tool installed by the manufacturer that periodically checks for updates?