Hi OP, I think it's important that you separate your anxiety around her food from her actual food. She will struggle far more over the rest of her life if you create a situation where meals become an anxious time for her.
First up, she's 25% for weight and 50% for height - that sounds like well within the tolerance for a normal healthy child. Every kid isn't meant to be on the 50% line! She is most likely absolutely healthy, you're doing great with chicken, fish, etc.
If she's not well and doesn't want to eat, there is no point in encouraging her - she may well vomit, which would increase her reluctance in a vicious spiral. Just keep her hydrated, and yes fruit juice is fine for that, especially if you dilute it slightly.
Once she's better, the things that worked well when mine were picky were involving them in cooking - there's a show on CBeebies called Big Cook Little Cook with recipes they can join in with (you'd have to pick an episode with a nice healthy looking recipe and get the ingredients in beforehand). My 5yo loves this, it's his favourite rainy day play, and he eats loads of whatever we 'cook'!
And the other thing is smoothies, we have a Nutribullet high speed blender and I get ground flax seed and nut butters and bananas and berries and raw cacao powder into them by calling it a 'chocolate smoothie' and DC help choosing the ingredients... Lots of fresh goodness that slips down easily, with a nice colourful straw.
But please try to manage your anxiety because long-term it could do damage to her relationship with food and her body. Best of luck.