How frequently can a word be used before it's considered repetition, in both spoken and written texts (details inside)

I think the title is a bit hard to understand, because I don’t know how to word it, so I’m going to provide the context for this question.

My friend and I were having an argument about word repetition while I was checking her answers for a couple of speaking questions for the IELTS. She wrote her answers down on Word and I was looking through it. The question was “what qualities do you think you need in order to be selected for a space mission?” So I corrected her document, and it read something like this: “I think there are three main qualities I need to go on a space mission. Firstly, I think I need high intelligence…” My friend told me to rewrite that because I repeated the phrase “I think”. I told her this is a spoken text, and beside this is the part of the exam where you have to answer everything immediately after it is asked, so you won’t have that much time to think about word repetition as long as it’s not serious, nor do anyone cares. She disagreed with me, saying that we have to avoid word repetition as much as possible to earn points, and that is what I’m here to teach her. I said it’s not possible to teach something that isn’t technically feasible in the first place. She still wasn’t convinced and kept telling me to change.

I thought about our conversation for some time. The conversation does provoke in me an interesting question: what is the line between a normal sounding conversation and word repetition? I know a lot of IELTS teachers tell their students to try to avoid using the same words too many times, but that is because the students need to show how much vocabulary they have and avoid making their texts sound boring. But if you are so focused on using different words every time, your speech will become extremely unnatural, which will certainly put the examiner off. But I still don’t know how much is too much. After all, this is a common problem with Engrish.

Who is in the right? My friend or me?