Can installing league cause computer problems?

So first of all, I have had not had this problem myself. Two days ago me and sister B convince sister A to install league of legends on her laptop. No problems immediately, but after two days sister A starts complaining that sending an email caused her computer to freeze up (she uses internet explorer). She blames this on the fact that she installed League the day before. I said that that's not how league works, that there's no way that it will interfere with her email as it doesn't use up bandwidth while its not on. Am I right in thinking this or is there a possibility that installing league (or any game) can have a detrimental impact on a computer/laptop's performance?
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