I too wouldn't be too concerned, DD1's weight can change from 1 day to the next depending on teething, sickness or overall activity.
Does she have a healthy appetite, is she active, happy, using her bowels 'normally' etc.. if so then i def would stress too much.
DD1 is going through a stage of not eating very well, she's got a cold, hardly touches breakfast, will snack little bits but not eat a lot of lunch or dinner, it's getting very frustrating but i'm putting it down to 2yr old attitude and not feeling well.