Hi,
I can feel how worrisome it would be if the child is not throwing up food and practically refusing to eat everything. I suggest, you must see a doctor and address the problem. I mean, not eating enough is a common problem with kids and one can then find solutions to it by may be changing the style of cooking, recipes, etc., but if the child is puking then I think a person who is a professional should be seen for advice. I think you take her to the doctor and see what he says.
Apart from that try changing the recipe of the food that you give he. I she is eating biscuits and puffs well, then probably there is some particular taste in the porridge that she doesn't like. Try avoiding any herbs if you are putting. And say, if you are feeding her sweet porridge all this while, try making it salty or visa versa.
Yueh Ru