Hi L.,
There were at least 2 other posters that indicated that it was not the responsibility of the complimentor to include all the children involved. I agree with this. You should not feel that both your children should always get the same things. They are not the same people. And, if your daughter wants to be noticed more, maybe you could teach her how to be more extraverted/outgoing.
When one of my daughters is complimented, and not the other, the other one steps out and smiles as if to say, do not forget me too. Now, we do not have this problem often because they are both beautiful in different ways. So, if one daughter gets it this time, the other one will get it the next time.
I do not want my children to grow up thinking that everything should always be equal and fair. It is not fair to them to trick them into believing that. They are coming to realize that they have to work for what they want, including compliments.
I also have a son, and he is the youngest. He is cute but he is rarely complimented for his dashing good looks. Instead, he works to be praised for his physical and academic abilities. (He sees how it works, and he is only 5).
Training children to have self esteem through defeat and failure will give them a stronger sense of self and success.
Your daughter should be proud of who she is, and so shoud you.
D.