Yeah you're right about the दूध and the veggie lasagne. It's never been directly stated on the tv दिखाना though but they do imply that she's vegetarian या 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 हाल का 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, आप can't really go द्वारा that on the दिखाना as the दिखाना 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 चीज़बर्गर at the Hollis bar.