Until she's 12 months the most important nutrients will come from BM... so you are doing a great thing by going back to demand feeding. I know Matilda lost weight around 8-9 months because of starting to walk & move around a lot more. She wasn't interested in solids at the best of times (and still isn't interested in eating) she loved her bottles at that time though. Matilda didn't put any weight on between 8-9 months and at 1 year was 7.8kg. She is almost 3 now and has only just reached 14kg. Very thin, but she eats when she is hungry and is extremely active.