Why is 1 Laptop dragging down internet?

Don't have the fastest internet speed but I can run my ps4 on psn online playing games online and it runs fine with a tablet, cell phone and 1 other laptop running on the Wi-Fi as well, for the ps4 i'm running direct wire Ethernet cable. But my mom's Lenovo laptop kills the entire network to a very slow crawl, my question is Why would 1 laptop drag down the entire internet? Its a slow laptop, anything I can do other than not use it?

It's infected with an alien virus. Kill by putting it the microwave for 10 minutes.

It can't be that slow-something else is amiss. Make a new wireless connection in the Network and Sharing center. Click to connect it and see if the problem is solved. If so, delete the original connection.