She seems to write code just fine. You are the one who had a basic principle being taught to them and instead of doing some critical thinking you opted to just re-ask the question and avoid the person answering your question with both an answer and a methodology.
tolower(x) will return a lower case version of x.
Thus:
switch(x) is still going to check x.
In other words, x is not lowercase-ified...unless it was lowercase to begin with
switch(tolower(x)) will check a lowercase version of x.
You should be able to comprehend now.