How to make a reluctant eater eat up

My girl is a reluctant eater. Its hard to get her to eat up her food. She will eat when I'm feeding her though. I'm really tired of this food war we have at home. Her brother loves food and loves eating on his own. He will eat up until he's full then tell you that he's full.

So one day I had this idea. I brought out the heart shape chocolate which the kids love and showed it to them. "Whoever finishes their food first, will get this chocolate" I said and you know what? My girl, the reluctant eater, finished her food all by herself in a jiffy. Lol!

I know I can't always use this method but it worked for the day. The other reason why I can't use this method all the time is because its unfair to the little brother who eats well but couldn't finish as fast as her just because he's younger. So although he didn't get to eat the heart shaped chocolate, I gave him a tub of yoghurt, which he loves for finishing his meal.

Does anyone else have a better idea than this on how to make a reluctant eater eat up? I hope you can share with me.