By plugging into the router you're only getting a better, more reliable connection than using wireless. Right now we have 3 computers wired to the router that stay on full time and anywhere between 5-8 computers connected via wireless. I doubt it's your computer being plugged in that is slowing their internet down. I'd blame it more on her getting a lower quality connection, low signal, from being wireless. If she wants a more reliable connection she can plug into the router too.