"Which one does she find?"
Translation:Elle trouve lequel ?
You only use "Est-ce que..." for yes/no questions, so you could ask "Est-ce qu'elle le trouve?"-- "Does she find it?" But if you want to find out which one, when, how many, etc., then you have to either use inversion, here "trouve-t-elle" or, informally, intonation with the same word order as a statement would have, "Elle trouve lequel?"
I believe yours translates to 'Who does she find?' If I remember correctly the phrase 'qui est-ce que' is used in questions to denote that the object of the sentence is unknown, but it is a person. In 'Laquelle trouve-t-elle?' the word 'quelle' directly translates to 'which' and 'laquelle' is 'which one'. This question implies that the unknown object is a feminine thing - like 'une pomme'.