I have had conflicting advice, some saying ignore her and let her go hungry, others saying insist she has some of her dinner as its important she gets a healthy diet.
The one battle you will never win with a child is over what they will eat. When it gets to the point of you insisting anything you are on a downward spiral. Unless you are going to strap the child down and lever their mouth open, food is only going to pass their lips if they choose to allow it. They have to ultimate trump card.
The more stress a child experiences around food and eating, the less that child will want to eat. We've all experienced being too anxious to eat. Now imagine that happening at every mealtime while someone punishes you for not being able to eat. It is no way to live.
It is our job as parents to supply a healthy, balanced diet to our children. It is their job to choose from that food the items they will eat. It is not our job to decide what they should put in their mouths.
My advice would be to decide what you are willing to cook each day, ensuring that there is something available for each child that they find reasonably palatable. You put that food on the table and allow/support them to help themselves and to control their own portion size.
You then sit together, talking about other subjects and eating your own meals without commenting on what they are eating.
At the end of the meal clear away without comment, offer fruit/drink of milk/ whatever else you feel is appropriate unconditionally. It doesn't matter what the children have already eaten if it's healthy food.
Don't encourage, persuade, cajole, reward, praise and most definitely don't punish.
This isn't an instant cure. Children's anxiety about food takes a good long time to go away. The most important thing is that they start to feel more relaxed and in control. Eventually they will cotton on to the lack of pressure and attention to their eating habits, relax and start to enjoy the social aspect of mealtimes.
Even if the range of food they will eat doesn't increase dramatically or quickly, it shouldn't get more restricted and everyone should feel happier and more relaxed at mealtimes. When they feel ready to extend their diet or try out new foods there will be no pressure or stress preventing them from doing so.
If they need snacks make them healthy snacks then it doesn't matter if they eat less at the next mealtime.