Internet very slow on one computer, but not another
Solution 1:
Great! Good job on plugging her computer directly into the router. As it's still slow then we can rule out wireless issues. The problem is with her computer itself. You don't say which operating system you're both using, so I'm going to assume Windows.
Unfortunately, more than likely it is a bunch of Malware causing problems on her machine.
Download some anti-malware software (like AdAware Free), install it on her machine, and run a scan. If you have problems installing or running a scan, her machine might be quite badly infected.
If that's the case, try running a free online virus scan, like Trend Micro's.
If you can't even load that site on her machine, then it's probably a really bad case, unfortunately. (Many Malware and viruses are programmed to recognize attempts to remove them or access anti-malware software.)
If this is what happens, then post back here and I'll try to give you some more help.
If everything comes back clean, then great. I was wrong and it's more than likely just a lot of legitimate programs taking bandwidth. To reduce the number of programs running, press Start/Windows Menu and click on Run. Type msconfig and load that program.
In MSConfig, click on the Startup tab and unclick everything (these are a list of programs that get automatically loaded when Windows starts -- they can be started manually at any time, and so probably don't need to be loaded).
Reboot the machine and see if any of the above has helped.
If not, post back and I'll try to help you further.
Solution 2:
Well after a very frustrating couple of days and no help whatsoever from customer service, I decided to try a different router/modem. I'm fairly certain she doesn't have any malware.
Luckily and inexplicably, a different router works just fine. It also helped speed up loading on my computer as well. I don't know if just the individual router was to blame, or the brand (Motorola).
Now everything is cruising along at blazing speeds with nary a hiccup. Thanks for all the suggestions, though!
Solution 3:
We had the same problem.
After investigating I found out that the slower computer was on airplane mode (win 8).
Once I turned it off it started to work just fine.