A friend helped me with this by offering a wonderful solution.

Variety. We started bento style lunch boxes. A few grapes/strawberries/fruit wedges, a few dried fruit, rice cracker, a piece of cheese or a splodge of yoghurt, some ham or cooked meat, some hummus and pita breads, sandwich sushi, or half a sandwich square, or even a tortilla/wrap with pb, a handful of dried cereal etc.

But variety. At dinner time on offer was what we had then fruit. I never got into the whole thing about two meals or forcing kids to eat it.

Pick the mealtime they eat the most to feed them their best meal. DS was always breakfast. He'd have fruit, toast and a handful of cereal and sometimes even baked beans or eggs. DD was always morning tea. She'd have her lunch then so id offer lots.

Remember they are built to listen to their metabolism. So long as they aren't filling up on junk, sugar or processed foods it doesn't matter when they eat their meal. And there is the old saying eat like a king for breakfast, a prince for lunch and a pauper for dinner. Kids do this naturally sometimes. As long as she doesn't have any deficiencies (this can cause loss of appetite), which I'm sure is covered by the multiv I'm sure she's fine. But go the variety at her best meal. Even if it's adding a piece of fruit and bread with dinner. Sounds weird but the more choice they have the happier they are

But whatever you do don't fight with food. There are huge links between this and emotional related food issues, be it under eating, over eating, or comfort eating.