No doubt she is normal, she must be very smart, too! What happens with children like that, according to linguists, is in their early years their vocabulary range in each particular language is smaller than monolingual children's in that particular language. However, if you count the words of the bilinguals (or trilinguals ;)) in all languages they speak it equals the monolinguals' vocab range! It can, of course, be compensated for when they are a bit older.