If i physically see some one cough or sneeze on my baby.. is there anything i can do to prevent her from getting sick .. or it's already too late?..

That sounds yucky !: All you can do is keep thoughtless people away from your baby, avoid taking baby shopping with you (people sneeze on vegetables, too, & some viral particles linger in the air), buy alcohol handwash & make sure visitors & family use it before picking up baby & hope that you passed along some immunity to that particular virus. As my kids' pediatrician said, "they're never old enough for k-mart.".

Too Late: Good handwashing is the single most effective means of preventing spread of illness.