Different ways you could say this sentence:
She's the most famous scientist in the world.
She's one of the most famous scientists in the world.
She's one of the more famous scientists in the world.
Somewhat incorrect: She's one of the famous scientists in the world. This is a bit confusing because you could use this sentence, but I feel like just not in this scenario. The reason why is that if you were to say that she is one of the famous scientists in the world, it means basically that there is some group of famous scientists across the whole world and she is one of the scientists in the group. Because there is no 'world famous scientists' group for the entire world, this wouldn't sound correct.
Here are some examples of where you could use that structure and it would sound more natural:
He's one of the popular kids at school.
I'm one of the tutors in our English class.
He's one of the lawyers at Doug, Co. Law Firm.
You're one of the chess club kids, aren't you?
You can see how in these examples above, there is a set group that they have to be a part of in order to use that sentence without 'most' or 'more'.