We're all missing the chance to chat about these things with other mums, see the range of 'normal' and pick up tips, and then once you've been worrying about something, it can feel like nothing is obvious.
She sounds a lot like my daughter was, happy to have 2-3 bites of most things, but that was it for carbs/protein. No problems getting through a whole satsuma though.
My daughter was breastfed, so I couldn't really control how much she had at a feed. We just offered solids before milk so she'd be hungrier for the solids and tried very hard not to push her to eat or show any stress – you don't want her to associate eating with stress. Things just slowly improved (with good days and bad days), and at 17 months, it's not something we really think about any more.
Some random other things that helped us: Try both eating with her and leaving her to get on with it. I always sat down with her, but if she hadn't eaten much, I'd keep her in her highchair whilst I pottered about the kitchen, and a fair bit of the time she'd decide to eat a bit more.
If you don't already, let her try whatever you're eating (except health risks, obviously). Food on from my plate is always better than food from her plate, and wee ones have some surprising favourites. My daughter loves curry flavours and, very randomly, kidney beans.
Notice the little wins. I remember telling my husband the wee one had really liked lunch, as she'd had 6 bites! (First sign of the taste for curry spices, as it happens.)