Matilda has gone through this a few times... especially when her teeth are bothering her.

My main saving grace is making her ice blocks where I use yogurt, bananas & some other fruit... and she will usually eat 2-3 of these in the days when she won't eat anything else. I think the cold numbs her gums & she loves that feeling. The other thing I have used when she's been sick & not eating is jelly. The Dr said to use it because it rehydrates them & she loves it too, it melts in her mouth so not hard to eat when they have sore throats or sore teeth.

Goodluck!