He put a hamburger in front of me and said 'it won’t hurt to have one'

I told my girlfriend openly that I’m on a diet and I’ve been paying attention for weeks. But last night she ordered a hamburger for herself and ordered one for me too. I don’t have to eat it, but she insisted, saying 'it won’t hurt just this once, are you going to say no?' So is this a conscious sabotage, or did she do this without thinking much? Did she act thoughtlessly, or does she really not understand me?