Hi,
It is worrying, but it is her nose that's the problem! Babies need to prioritise breathing over feeding if their nose is blocked. She is not self weaning - at 9 mnths she is too young for that. However, if you give her formula you may well wean her inadvertantly. How is she eating? Solid foods? You can give her extra solids, or like many of us when we are sick we like cold things - icecream, jelly (you can make with fruit juice, iceblocks etc) She seems to have been sick for a while - it might be worth taking her to the dr if you are worried - put your mind at ease if nothing else, and get the right treatment if there is a problem