Does anyone know how a Mac and a Dell can interfere with eachother?

Ok well I have a dell computer, xbox live, and everything always works fine. However, when my sister comes home from college with her Mac, the internet goes crazy. I get kicked off xbox sometimes, and the computers lose internet frequently. What is causing this struggle between the computers? And if you know, any suggestions on how to fix it?Does anyone know how a Mac and a Dell can interfere with eachother?The signals from the internet. Ask your sister to use her laptop in a different room and see if it makes any difference.

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infiniti g37