My daughter goes through phases of eating next to nothing, I just don’t make a fuss and give her what I know she will eat even if it’s just a yoghurt x

Yeh both mine go through this occassionally. Nothing much can you do but continue to offer. I don't give any treats/ puddings if they don't eat a decent amount. If their complaining they're hungry they can help themselves to the fruit bowl.

Theos always been like this. We have just stopped fighting, he's offered food and if he is hungry he will take it, we don't offer him things like crisps, chocolate, cake, ice cream or any sweet snacks other than fruit. He gets offered three meals a day and If he doesn't eat then that's fine. Easier said than done but don't get to caught up on her food intake, she won't starve herself, if she knows shes not going to get the sweet stuff and she's hungry then she'll eat what's offered eventually.
Another thing we've found is if we try to encourage theo to eat when he isn't really interested then he's less likely to eat, so we literally just leave him to it, his dinner is on the table but if he wants to run around and come back and fore then we let him. We don't make a fuss if he eats a whole meal and we don't make a drama if he doesn't eat anything. It's a tricky mind set to get into at first, but you just have to remember that she won't starve :) x