Can't load sites through all browsers (but can mostly when adding `https://` manually)

Question

So my friend contacted me today and begged me for my help. She works at a designing company and said:

"Since last week, I can't load any site excluding google. When I type the site name in any browser (IE/Edge/Firefox/Chrome) the blank page just keeps loading and nothing appears. I already called my IT guys and they formatted my computer a few days ago, and the problem re-appeared after the format."

She also added that there are a few other employees at her place (which are not connected to the same network but do speak with each other via emails) have the same issue. I tried helping her via Teamviewer. I'll try and post all my findings while trying to help her, and hopefully someone will know what the hell is going on with her computer:

1. As already mentioned above, the main problem is that all browsers can't load pages (except www.google.com). After waiting a certain amount of time, the browsers show Error: Connection failed or Error: Connection timed out exceptions.
2. When manually adding https:// to URL, the web pages seem to be loading as usual, with no problem
3. There is no apparent DNS problem. I've tried pinging to various domains and received IP addresses (haven't checked their authenticity). Also, Just for verification I've manually set the DNS servers to 8.8.8.8 and 8.4.4.8 but the problem didn't disappear.
4. I've tried looking at some network connections via Wireshark. From what I've seen, every browser tries to first connect to the domain via HTTP. It seems as though the domains don't forward the browsers to HTTPS addresses (no forward request was sent from any domain, and no connection to port 443 has been made).
5. The computer is connected to the internet through a WiFi connection. I've tried connecting to various different networks and even asked her to turn on her 4G Tethering and connect through it. The problem hasn't disappeared.
6. I've connected to another laptop of hers, which is connected to the same WiFi network as the problematic computer. The laptop works fine and has no apparent problems while working on all web browsers
7. I looked at her Internet Connection Settings. She isn't connected to any proxy, nor a VPN of some sort.
8. I've downloaded the Sysinternals suit from Microsoft's website. I executed the Process Monitor and the Process Explorer with a slight hope of catching some fishy process. From my brief experience with malwares, they tend to enter sleep mode or even kill themselves when either processes appear. That didn't help.
9. I've looked at all of her recently installed software. There was one software from a developer in the name of "InfoSoftware". After googling that name, I suspect that might be some kind of a malware. I've removed the software but that didn't help. There was also another program called "NetSurveillance". I removed it too just to be sure, but that also didn't help.
10. I installed ad-blocker plugins on Firefox and Chrome, with no luck.

Because the nature of the problem is so isolated to a single computer, with only web browsers being affected (from what I saw), that leads me to think that she might have go infected with some kind of a malware. Maybe her co-workers too. I would really love if you guys had some expert suggestion or leads at might be going on here. Thanks in advance!

UPDATES:

1. I deactivated all of her anti-viruses programs and her firewall protection for a brief moment. I wanted to make sure no outbound/inbound rule was the root of this issue. Didn't help.