First, her eyes were like o_o, and then, they become to O_O. >She made sheep's eye at him Stupid look without understanding, I guess.

It means to look shyly and admiringly at someone. She may make sheep's eyes at him when she is "lovesick", or so overcome with devotion that she doesn't behave normally. Her vacant expression will resemble that of a sheep.

This is a phrase. make sheep's eye at Sb. = 向某人拋媚眼。

It means she loves him !