Yeah you're right about the 우유 and the veggie lasagne. It's never been directly stated on the tv show though but they do imply that she's vegetarian 또는 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 recent 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, 당신 can't really go 의해 that on the show as the show 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 치즈 버거 at the Hollis bar.