she does not need topping up
the vast majority of babies , whether ff or bf, have a growth spurt around this time, which is why sometimes it seems like the right time to introduce solids
but a good extra milk feed is far more calorific , nutritious and filling than a spoon or two of puree
also, after being poorly , most babies, whether ff or bf, will make up for lost time as you say, and feed a lot more frequently
your milk can satisfy her now, and next week, and next month, and until she is ready to wean, if that is what you choose
losing weight especially after illness is not that much of a surprise, but also weight gain plateaus...
try not to worry and keep on doing what you are doing