Is your wifi-signal strong enough?
Is her wi-fi protected? (as theabyss27 said in your other thread)
You also might want to run a test on www.speedtest.net to check if her download/upload aren't good enough.
If those other are all true, ask if you can install an app named netlimiter (free version is enough) on her laptop so you can look if her laptop doesn't take all the available bandwidth. You can do this on your own laptop as well.
