Translation:Perhaps she had found out something.
They are exactly the same in every respect.
quizá = quizás
They have been in the dictionary since the 18th century, but at that time "quizá" was considered to be its original form. They have both been used indifferently both formally and informally for the last two centuries, though.
They are adverbs, and as such, they don't agree in gender, number or person with anything. If used at the beginning of a sentence, both indicative and subjunctive are used (although the latter is preferred) depending on the degree of confidence. If they are used after the verb, indicative must be used.
Thanks for the good explanation, though I also agree with the comment by JJvH1991 about the distinction being unclear in the sentence. Putting your thoughts together, it seems that "uncover" should also be accepted, while the English cognate "discovered" should remain as an unaccepted response.
I disagree with "discovered" not being accepted as many things intellectually or informationally can be discovered. For example, "I discovered why she was mad at me" or "They discovered the concept of math." So I think "discovered" definitely works here. That being said I do agree that "uncover" should also be accepted. "They uncovered the truth" or "I uncovered the reason behind her behavior" are examples of how that can be used with abstract concepts.