TIFU I messed up by trying to "repair" my girlfriend's laptop

So, by the way, "this didn't happen today but literally three days ago, and I'm still on the couch."

For the past 1-2 months, my girlfriend has been working on her master's thesis. It is a 100 page monster about some super niche topic in environmental policy that I barely grasp, but she has put every bit of her heart into it. She has been worried about losing it, but, like a true academic, she always kept postponing it. The file only existed on her old MacBook, which was so slow that it was like a tortoise on tranquilizers.

Last weekend she told me that the laptop was "practically worthless" apps crashing, the death beachball every five minutes, the works. Being the supportive and (slightly tech-savvy) boyfriend I am, I proposed to "get rid of the junk and clean up in no time." She was reluctant at first, but in the end, she passed it on to me with that trusting smile that now haunts my nightmares.

To start, I went through the common procedures: cleared cache, removed some old downloads, and let Disk Utility run. It still was slow. Then I got overconfident. I recalled reading that, by disabling some of the system extensions, the old macos version would be quicker in some cases. So, I opened Terminal, copied a command I found in a random forum (yes, I know, rookie mistake #1) and hit enter.

The laptop crashed. Completely. I force rebooted it… and it came up in the recovery mode with a huge sad folder icon and a flashing question mark. That was a typical "no bootable drive" error message.

Panic level: slight. I searched on Google, used Internet Recovery, played around with Disk Utility once more. After that, I noticed that her main drive was shown as gray and was categorized as "not mounted." In my limitless sagacity, I thought "perhaps I could just delete macOS and then reinstall it and restore from time machine." But… she hadn't ever activated time machine. Therefore, there was no backup. At all.

To cut a long story short: after four hours of progressively more desperate tries, I eventually came to the conclusion that I could not win this time and so I took it to the Apple Store Genius Bar. The conclusion? The drive was so badly damaged that it was beyond repair, and the data was gone. All of her thesis, research notes, references, everything gone.

When I applied the news to her, she did not shout. Instead, she became silent, staring at me for ten full seconds, then saying, "Okay." After that she went to the bedroom and shut the door. Since Tuesday she has been at her sister's place.

Currently,I am gifting her the most up to date MacBook Pro as a token of reconciliation, I am installing automatic cloud backups as if my life depended on it,and learning firsthand that "helpful" does not equal "qualified."

TL;DR: Attempted to speed up GF's slow laptop causing accidental erasure of her hard drive, deletion of 1-2 months of thesis work with no backup. Relationship status: pending.