Define "left". The crop is on her "the chickens" right side, or your left as you face her.
How old is she? How long have you had her? A crop can get quite large normally, is it just that you aren't used to it?
Check her in the morning, before access to feed, is it still there? Is it solid? Gravelly (like a mass of pebbles)? Mushy? Watery (like a half inflated water balloon)?