The fact that κάμηλος can be masculine or feminine without changing declension exhausts the Greek content of this question.
As for why the camel in Matt 23:24 is feminine, I consulted several commentaries and ... nothing. They don't even notice. If there's something particular about she-camels in this culture, I don't know what it is.
Stephen C. Carlson, Ph.D. (Duke, New Testament)