The correct option is
A Either
The conjunctions, 'either .. or' and 'neither ... nor' are used in pairs and are called correlative conjunctions. 'Either ... or' is used to make a comparison between two ideas, and only one of them will happen. While 'either' has a positive connotation, 'neither' holds a negative significance.
There are two nouns in the given sentence viz. 'Kanu' and 'her brother'. However, the verb, 'has won' indicates that the subject of the sentence is a singular noun. Hence, only one of the two nouns is the subject. In such statements, the correlative conjunction, 'either.. or' is used. We can also see that the word 'or' is used in the sentence. This is a clue that the appropriate correlative conjunction which can be used is 'either'. Option B is correct.
Option A: 'Neither.. nor' is used to make a negative statement about two nouns. 'Neither' always appears in a sentence along with the word, 'nor'. The word, 'nor' does not appear in this sentence. Hence, option A is incorrect.
Option C: The conjunction 'when' means 'at' or 'during the time that'. It denotes the time of a particular action. The clause beginning with 'when' should be followed or preceded by another independent clause. In this sentence, there is only one clause. Hence, option C is incorrect.
Option D: The conjunction 'so' is used to show the reason for something. In the given sentence, there is no word indicating that it is conveying a reason. Hence, option D is incorrect.