Why Does mid 2010 Macbook Pro have WiFi Problems?

First step is to try her computer with an Ethernet cable to her router and test the network performance, if that is OK then you can fault find the WiFi. Obviously if the Ethernet is slow and problamatic you wil need to fault find on her computer, perhaps not enough memory, low disk space, one application using all the cpu etc.

If it is WiFi only problem use a program such as WiFi Scanner (from the app store, others avaible, you could use your machine) and test for other WiFi networks interferning with the network at your girl friends. Also suspect bluetooth and anything that is on the same frequency as the WiFi

Although your computer works well, any interfernece may cause problems with your gf computer.

What exactly are you seeing? You said they both pass speed tests with about the same results, and that hers shows the same behavior wired or wireless. What's it doing?

This is why I thought you'd tried wired already:

The problems exist whether she is connected to the network directly out of the Pace modem / router, or the Airport network.

Try turning off bluetooth or changing the wireless channel. Wifi can be a royal pain to troubleshoot. You'll see all kinds of suggestions on here. I also have a mid-2010 and ended up fixing my problem by changing the wifi cable internally. My symptoms were a little different though. I can tell you that if you're unable to track it down, this works well. It's a bandaid, but it solves the problem. I used this temporarily.

http://www.amazon.com/gp/product/B003MTTJOY/ref=oh_details_o02_s00_i00?ie=UTF8&p sc=1

There is different hardware for the two connections and it could be the WiFi in the computer that has a hardware fault, but if the ethernet is slow and problamatic we can forget about the wireless and look at other items in the computer.

Even if it only affects WiFi, your computer probabaly has a different wifi chip and may perform better under adverse conditions.

You don't have both the Pace and Airport running as wireless networks, do you? That can cause problems by itself. If you're going to use the Airport as your router, you should disable the router functionality on the Pace device and only use it as a modem. You've got your own little broadcasting station going on right now if that's the case.

Normally you do a bridge when you've got a large area to cover. Then you put one on either end, cable those two, and you get a steady signal as you move around. It makes no sense to me at all to bridge two devices that are next to each other. I'm not familiar with that provider so I don't know what their equipment is, but anytime I've set up another router to replace the original, I've disabled the original and only used the modem portion. My guess is your tech didn't know how. If you can connect to either of them, I have to wonder which is handing out IP addresses. I guess it can work, it just doesn't seem to make any sense to do it that way. One problem you'll have is that if they're both handing out addresses and you connect to one and she to the other, you won't be able to see each other on the network. Not to mention if you've got a wireless printer or something.

All that said, when you get to her machine take a look at the "fan" icon that represents wireless strength and see how it is. Also make sure those 2 routers aren't both using the same channel. On the Airport, use Airport Utility. When it connects click the Airport picture then Edit in the popup window. Click the Wireless tab, then Wireless options. If they're both on the same channel you'll have problems. Some machines also seem to have issues connecting to the 5mhz band. You get around that by giving that band its own name then connecting to the other band. In other words if it's currently named Spot, you name the 5mhz band Spot 5mhz or something. It's in that same window.

It'll probably work just fine cabled. That's a totally different medium, but what do you do if it works well? Leave the cable connected?

MBP wifi can be a bear to troubleshoot. That's why I suggested that little USB dongle. It actually worked great, I just couldn't leave it alone. Anyone but a computer nerd would have been totally happy with it. That said, here's a starting point.

http://support.apple.com/kb/HT4628

One thing about the Airport is that you can hook up a hard drive to it and do automated backups via what Apple calls Time Machine. No one worries much about it until their hard drive crashes, then you see the frantic "Help! I've lost all my data" posts. I'm just saying it's not a bad thing to have, and I realize her problems started before you got it. Try the link and see how it goes. There are tons of posts on here for troubleshooting wireless, and it can get very involved. Everything from what I suggested to creating new locations, etc.

Yeah, a couple things if you're going to do that, which will definitely improve wireless in the house... you need to cable the two together and make sure they're on different channels.

On the dongle, if you go that route... they ship it with one of those mini-disks. Don't try to stick that thing in a Mac. Just go to the website and download the driver.