I would say teeth, brewing illness, or just a phase. It happens here occasionally. My take on it is children won't let themselves starve so I keep offering the normal amount of normal food that know she would eat when 'well' (for want of a better word). If she starts throwing it I just take it away, no fuss, maybe something like "oh I see you must be finished because you are throwing your food" - but not getting cross. Then offer what I would have offered for dessert anyway e.g. a yoghurt or fruit (try to stick to healthier things if appetite is low). But nothing extra. No alternative for main course and no extra pudding. No extra snacks either, just the usual. If she gets hungry she will eat - if not at this meal then the next.
I know it can be stressful but I think it helps to have the mindset of 'I'm not going to get into a battle about food'. I very much see my job as providing DD with a varied and nutritious diet and the opportunities to eat it. It is not my job to make her eat it - that's up to her. If she eats, fine, if she doesn't, also fine. Children are so quick to pick up on when we are stressed and the last thing you want is for this phase to become a long-running battle as you said.
