Our 21 month old is spotty with meals (despite having been above the 90% in weight since birth).
Both of our kids are getting to be more difficult at dinner time because their attention is usually elsewhere instead of on what they're eating. Our son is always a big breakfast eater, or daughter-not so much.
We have a rule in our house (that we can really only get our 3 year old to obide by). We'll give a few options for dinner based upon meals we'd already be making. Regardless of what's made, he has to have a few bites before he may be excused. We never make him overeat (he's been a snacker since birth which I prefer), but he can't sit there and not touch his dinner just because he's distracted. We have lots of heated, uncomfortable tantrums (by Mom, Dad and son), but in the end, he has to do what we ask him.
We also try to offer healthy snacks as much as possible (though we have plenty of other, not-so-good things for occasional snacking, too). The past 2 nights, he asked for a banana w/peanut butter when going to bed.
Maybe changing what kind of seat she's sitting in (letting her do more of a "Big Girl" type thing, or letting her pick her plate, letting her help you "prepare" the dinner might make her more interested.
We also have problems with our kids snacking between getting home from Day Care and when we sit down to dinner that dampens their appetite.
Good luck. Has anyone warned you that 3 is the new 2?