Are you using vitamin drops? If you speak to HV they might advise one containing iron, as that's what she will be most in need of.
If she likes yoghurt, would she eat a creamy baby porridge with added iron? If you make it up with breast milk to start and serve it tepid?
Maybe mix a fruit pot (no added sugar) or pureed fruit into her yoghurt, so she is getting some fruit.
My 14moDD is not a great eater but if I keep offering the same things, usually she will eat bits of things. She really loves things like avocados, nut butters and houmous on wholemeal toast and chicken cooked in the slow cooker so it's really soft.They're all quite bland but nutritious and high in calories, which is what we want atm.
I am still bfing and she is definitely more receptive to food when she hasn't had milk for a couple of hours, although it is hard to get the balance right, because you don't want her to be too hungry.
If your DD expects yoghurt on the spoon, could you pop tiny pieces of the new food in her mouth for her to try?
DD currently likes to 'feed' me then take a bite herself, so she ends up eating more when we play this game(sneaky)
It is so worrying when they won't eat. Hope she gets a taste for more things soon.