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 wifi as well, for the ps4 im 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?

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