Is "While" a relative pronoun?

"She came to visit me, while I was sleeping". While in that sentence is a conjunction, meaning "during the time that; at the same time as". There should not be a comma after it.

For your sample sentence "while" Begins a simple adverbial phrase that tells "when" you were sleeping. No comma needed anywhere in the sentence.

I think the you are looking for use of "while" when it is used to make an a contrast or objection.

He liked the blue car, while I liked the red one.

"While" isn't used as a relative pronoun; it's used as a noun, conjunction and transitive verb. Some northern Brits use it to mean "until."

Thank your for replying and correction. I know that 'while' is used as a conjunction but I was very much surprised when the English tutor presented the above sentence as an example of relative pronoun quoting 'while' as a relative pronoun. I stood up and asked him whether the word 'while' is a relative pronoun and he said yes, I was totally puzzled by his response and thought that he was the tutor and there must be something. So, I am trying to clarify my doubts.

Thank your for replying.
I know that 'while' is used as a conjunction but I was very much surprised when the English tutor presented the above sentence as an example of relative pronoun quoting 'while' as a relative pronoun. I stood up and asked him whether the word 'while' is a relative pronoun and he said yes, I was totally puzzled by his response and thought that he was the tutor and there must be something. So, I am trying to clarify my doubts.
Though I am not very proficient in English Grammar, I know sentence structures, a little bit of grammar, so sometimes they (tutors) keep us puzzled when they present a wrong statement for eg. The English teacher who taught us for a few days only, (before the tutor I mentioned in the above paragraph) presented a sentence with the word 'Tantrum', - The baby was throwing tantrum (something like this, I forgot the sentence), he explained the meaning of tantrum as - the baby was throwing things like toys etc. Ironic!

The baby was throwing a tantrum. The use of 'throw' in the example given might lead to confusion, since one can throw (have) a tantrum, or a fit, without physically throwing any object. An angry child throwing a tantrum might simply lie on the floor or ground and scream.