Actually, "wide" cannot be an adverb, until it is modified into widely. Common usage would be to say: "He opened his mouth wide." But it would be incorrect, the correct usage being "He opened his mouth widely."
Quote:If wide is used as an adjective in Yoong's sentence it would have to define the eyes themselves meaning they were wide as opposed to narrow.
That is precisely how it is used. Both "wide" and "open" are used to describe the old lady's eyes. Neither word is used to describe or modify the action of a verb.
An adverb can be used to modify an adjective, as in "extremely tall," but adjectives do not become adverbs, or even adverbial adjectives, without being modified, most commonly by adding the suffix "ly." (I am just being cautious in that statement--it were possible that an adjective could be modified in another manner to become an adverb, but i can't think of any other example than the suffix "ly.")