Yeah you're right about the latte and the veggie lasagne. It's never been directly stated on the tv mostra though but they do imply that she's vegetarian o vegan sometimes. She's also worn some vegan clothes and Ezra mentioned something before about going to a vegan restaurant with her.
EDIT: In the most recente episode, Aria tells Jake that she doesn't eat meat so it's confirmed that she is vegetarian.
Although it does say she is in the book, te can't really go da that on the mostra as the mostra is often vastly different than the books. I mean, in the books, Emily is a freckled red-head whose hair has been turned kind of green and fried from all the chlorine in the pool. However, it is alluded to in the series several times; and she also tells Jake she doesn't eat meat. In the pilot episode though, she orders a hamburger al formaggio, cheeseburger at the Hollis bar.