Without some actual details its tuff, you said it works fine on other wireless networks.. And other wireless user in the same room not having any issues.
Slow pages often point to dns like mentioned, but I would have to assume she is using the same one room mate is using - so that doesn't make a lot of sense.
I would look to see if she is connecting with say B, and room mate is on N or something.. Some basic details of the school network would help, are they B, G, N -- do they support 2.4 only, or 5 as well?
Could be her laptop/wireless card has an issue with the security being used. Is it WPA, WPA2 with tkip or AES, while room mates laptop has no issues. The type of network and encryption would most likely be different on different networks, so could explain why its fast on those.
Quite often schools use some sort of endpoint security client like cisco, etc. Her machine could be having an issue with that, which again would not be used on other wireless networks.
edit: Proxy thing seems unlikely because room mate should be on same one, etc. But maybe she should be using proxy and is not, or vice versa room mate is not using proxy and she is?
edit: jaredfrost has point about AP, but I doubt they would hard code to use specific one.. But sure she could be different one that is overload while room mate on other side of the room is on different one.. But normally dorm rooms are pretty tiny
So that seems odd that they would not be on same AP
But all good points - its very hard troubleshooting something like this without being there and details. There are SO MANY things that could be wrong.