The correct option is C And
The given sentences "He doesn't like her" and "she doesn't like him" are independent in meaning and when they are joined together, they are merely added to the other. Hence, a cumulative conjunction is used, 'and' is the most appropriate conjunction as it merely connects these sentences, without altering any words. Thus option B is correct. 'But' is an adversative conjunction (contrasting conjunction) that connects two sentences which are contrast in meaning, for example, "He doesn't like her but she likes him". As the given sentences are not contrast in meaning, option A is incorrect. 'If' is a conjunction used when one of the clauses or sentences is a condition, example, "He will like it if she behaves well", the condition here being "behaves well". As none of the given sentences are conditional, option C is incorrect. 'Although' is a subordinate conjunction that combines two sentences that are contrast in meaning, and one of them depends on the other for its full meaning. Since the given sentences are neither contrast nor dependent on the other, option D is incorrect.