Could be specific to the computer, or the wiring (either the cable, or even the port on the router)
For your computer specifically, what kind of hardware do you have? If it's not consistent across the computers (for example, if you have 10/100 and your sister has Gigabit) then you can;'t compare apples to apples in the results.
Are your drivers up to date? That should probably fix it, if the hardware is the same.
If drivers are up to date, and you're sure the hardware is the same - test your sisters computer in your location and test yours in her computers location.
It could be hardware, driver or even cabling related. Which router do you have? Which port are you connected to?
Some only have X number of Gigabit ports, and if you're connected to secondary ports, you may only have a 10/100 connection.