Analyze the given information and answer the question on the basis of it.

Five girls – M, N, O, P, and Q were comparing marks they scored on a test. It is known that no two students scored the same marks. 

It is also known that O scored neither the highest nor the lowest marks, nor did M score the least marks.

N had three persons who scored less than her.

P and Q were separated by the lowest possible difference in their marks.

Who scored the highest marks?