Why did Lavan send his daughter Rachel to shepherd the sheep and not regular shepherds?
Targum Yonasan: Lavan's flocks were struck by a plague and most of his sheep died. The few sheep that remained he gave his daughter Rachel to look after.
Why did Lavan make Rachel the shepherd, and not Le'ah?
Ramban #1: He did not appoint Le'ah to look after his flocks, since her eyes were 'tender', and the sun 1 would have caused them damage.
Ramban #2: Because Le'ah was older and fit to get married, and he was concerned for her safety. 2
Chizkuni #2: This was to honor her older sister.
Tosfos ha'Shalem (28:8): Leah was more beautiful than Rachel. Lavan hid her in inner rooms.
Seforno: Rachel was knowledgeable in the art of shepherding.
Why must the Torah say that Rachel is a shepherd? This is obvious. She was coming with the flock!
Moshav Zekenim: It teaches that even though she was a shepherd 1 and in the heat of the sun, which blackens, she was beautiful.
Seforno: This teaches that she was knowledgeable in the art of shepherding
Seemingly, one might have thought that she was not a shepherd, and due to Hashgachah Pratis today she tended the flock! (PF)