A doctor told me that they'll still get colds etc when BF'd, it's just that it's much less likely to become bacterial and require antibiotics.
For my 2c worth, DS1 never got sick as a baby (he didn't start daycare till he was 12 months) ... DS2, on the other hand, had colds from about 4 months of age - thanks to his big brother bringing the germs home from daycare and/or when the weather turned cooler.

Keep up the great work you're doing MM - hope your DD is better soon.