I also find my LO has hungry days and not-so-hungry days. They are very good at self-regulating what they need - so even though you know she might easily eat 10 spoons some days, it doesn't mean she needs to every day. I was told to look more at what my LO was eating over the course of a week, rather than a particular day. I planned meals as a whole (and still do), so I often did offer a small piece of fruit/yoghurt etc after the rest of the meal, but I offered it whether she'd eaten everything else or nothing - it's not a special option because she hasn't eaten, iyswim.
And as Catherine says, milk is the most important source of nutrition at this age. Basically if you're offering a variety of healthy foods and your LO generally tries stuff and is happy and active, I wouldn't worry at all!
xx