Not sure where you are and what types of foods you generally eat but there are a huge range of things you can offer for breakfast. Many people use oats porridge for breakfast which can also be made into a 'cake' to be eaten as finger food rather than spoon fed, I mostly served baby muesli to mine (mixed thick and served as finger food balls to be either picked up or stabbed with a fork to eat) and now he eats (no added sugar or salt) adult muesli which I soak in milk over night to soften the grains.
For quite a long time I served mine a 1 egg omelet for breakfast, this was on advice I gained on the BW boards, my DS was reluctant to eat a good amount of protein later in the day but amazingly he would eat an entire egg at breakfast time and didn't even complain that his muesli wasn't there! Many LOs will eat things at breakfast which they are fussy over later on in the day, perhaps because they are very hungry at that time and glad to get a good meal
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So breakfast ideas:
Eggs are great - omelete, hard boiled, scrambled, french toast (eggy bread, you soak the bread in whisked egg then fry), adding protein to your LOs diet would be great.
Sausages - although processed some of the better quality sausages are pretty good, some butchers will make up a batch of sausages for you to your request, with no added salt and with whichever cut of meat you choose, these are likely healthier. If you didn't fancy the idea of sausages you could try making a kind of meat ball at home from fresh meat
American pancakes - made with fresh bananas in the batter mix or with other fruits added
toast - with spreads such as butter, pate, nut butter, houmus, cream cheese
bean burgers or lentil burgers, falafel type patties made from beans/lentils and veggies
...really you can offer anything at breakfast, fish, meat, veggies, it is up to you.
Here's a thread which has lots of finger food ideas for snacks
Finger Foods (6 months+)I used to make batches of pancakes, mini muffins, bean burgers/patties, mini meat loaf/burger, oaty chews and things like that, I'd freeze them interwoven with baking parchment so that they didn't stick together, then I could lift a couple out and they would defrost during the morning and be ready to eat (cold) at snack time or for picnic lunches.
If we had left over veggies from our evening meal I kept them in the fridge over night and served those up for snack the following day.
I also gave things like fingers of cheese, canned beans (such as pinto beans pre-cooked in water no salt or sugar added, I just drained them, used a portion for a snack and then used the rest of the can to make bean burgers or to add to stew for dinner etc).
Humous or other bean dips/spreads are easy to make if you have a blender and are a great source of protein too.
Fresh fruit is a super easy snack to offer too.
I know you are concerned about her losing weight, I would really think at this age the focus needs to be on adult foods, protein, good fats, a range of veggies and fruits so that she can access all the vitamins and calories a balanced diet offers. I imagine she would put more weight on with the more grown up diet, she might also be more interested in the food if you try her with different things.