I have a 19 almost 20month onld that just doesn...

I have a 19 almost 20month onld that just doesnt want to eat. I can offer her food unitl im blue in the face but it doesnt make a difference. She never really beena big eater and is very skinny (although tall for her age which doesnt help) i have peadeatricians having a go and i dont know what to do. Our cupborads and fridge are always full to overflowing and there is constantly food on offer but she only nibbles at 1 maybe two things and then wont have anyhting for hours and hours. SHe only has 2 1/2 milks bottles a day and drinks water. Any suggestions would be fantastic. Im hoping she will grow out of it.