Another brother or sister?

Is frustrating to think when you believe that your family is completed , without problems , without liar and with the members that you meet, suddenly our father tell us that he has other daughter.

Would be painful thinking about my reaction, well, all depend, l mean, if the girl is order than me would be less terrible, but if she younger l' d feel really disappointing and jealous because l' m the little girl in my family.