Unfortunately a MacBook Air, doesn't have an ethernet port, so she would have to get a USB -> Ethernet adapter to try that.
So I found a You Tube video that deals with this issue. I watched it and it seems like a legit video. But don't have a MacBook on me right now to test it. If you are still having issues I can get a MacBook tomorrow and try it .
https://www.youtube.com/watch?v=FydtdMJ4BGM
What he suggests in the video seems plausible since the config files that are modified do control many aspects of the wifi network card performance.
Good Luck