Food shouldn't replace milk at that age - not until closer to 12 months. So if her milk intake drops then she needs less solids - that's the best way to know. Some babies are really slow with solids and won't take more than they need but others will keep eating and then not have enough milk. At that age she doesn't need food at all, it's just about learning tastes and textures, so I'd stick to small amounts for now.