Boot problems - 2 boot partitions, 1 damaged (I think)

I'm new here, and not sure if this is the right place for this post. Please tell me if I should post this elsewhere. My partner's laptop has a boot problem that I've half-fixed, but I think it's causing problems with updates (and it's really annoying). She has to interrupt the boot process by pressing F12 repeatedly to get into the boot menu and select a 2nd boot partition (it looks identical to the first in the boot menu).

To start at the beginning - my partner's running an Acer laptop with Windows 8.1, but several months ago it froze during a Windows update. It was saying something along the lines of "Installing updates, Do not turn off your computer, it will be automatically shut down when finished". Problem is the computer just wouldn't shut itself down. We waited about 48 hours, there was no sign of activity, and the computer wouldn't respond to keystrokes like Ctrl-Alt-Del. With no other options, I hit the reset button on the laptop.

The laptop just wouldn't boot up after this - the Acer logo came up then it would turn itself off and back on. I booted from a USB stick into a version of Linux that was supposed to be good for file recovery and was able to back up the entire hard drive. Then I booted from a recovery flash drive and tried to refresh the PC, but it said "Drive where windows is installed is locked". I tried a bunch of things I can't remember to find out what was going wrong, but I eventually got it to boot into Windows again by following this YouTube video.

Something went wrong during the process he describes in that video that he didn't cover, and as I can recall I managed to get around the problem by following some part of his instructions for fixing the problem in legacy (non-UEFI) mode, either on another of his videos or that video's accompanying text on GitHub. And I don't think I managed to finish the steps he gives for UEFI mode.

It boots now, but only if you select the 2nd boot partition in the boot menu (which I assume is what I made by following the video(s) above). If you don't do that, it just turns off and on again after showing the Acer logo as before.

I don't know much about boot partitions and would love to get some advice on how to stop this. I assume the original boot partition was damaged and I have created a 2nd working boot partition. I don't know if I can just delete the original boot partition, or if there's something else I should do.

Here is a screenshot of the Disk Management window showing the current partitions:


My partner can't install any updates now, and she wants to install Windows 10. I have no idea if this is related to the boot problems, but I want to fix them anyway and I'll see if updates work after that.

"If you need to install or reinstall Windows 8.1, you can use the tools on this page to create your own installation media using either a USB flash drive or a DVD."

https://www.microsoft.com/en-us/software-download/

When you perform a clean installation using a USB or DVD, the Windows 8.1 setup will auto detect the Windows 8/8.1 product key from the firmware chip and automatically enter it.

On the "Where do you want to install Windows?" screen delete all the partitions and then click the "Next" button.

Thanks for your response, Osprey. I really want to avoid doing a clean install of Windows if at all possible. She has a lot of software and other stuff on the laptop that would be difficult to restore, but I'll keep it in mind as a last resort.

Does anyone know any way I could recover the laptop without doing a clean install?