@Lauren I'd say she's drinking her usual amount. It's hard to pinpoint when the eating got like this as she's in nursery but they haven't mentioned anything about her eating. If it doesn't pick up in the next couple of days I'll contact the GP. I did manage to get her to eat some roast dinner, so hope it's getting better!
She sounds poorly to me. Is she drinking much? If not definitely call the GP. You could try just offering snacks regularly like yoghurt, biscuits, cheese. A couple of days of poor appetite won't cause harm but I'd be seeking medical advice if any longer