S.; first of all your child is two, most two year olds are asserting their own mind, and in the old days it was called the terrible twos, take heart and dont think its the other child, in fact the opposite may be happening when you separate the two, instead of her feelling special for the alone time, it may be feeding her to not like her sister, and that she has to do things alone, its ok to incorporate her into the youngs ones life too, and she with your patience and love will endure this, my oldest did this, and did not quit till almost 4, for the most part they are good and happy, but every now and then they are stubborn and strong willed, you have to remain consistant to get her through this spell, consistancy is the key, make her be the big sister and do things with her sister, and involve her too, and be balanced in the alone time and family time, but also know that its been said that a child that goes through the terrible twos, also are great teens and go through that phase more easily, especially with consistancy, cause they have learned how it works at a young age, and dont try to assert themselves as teens, this did prove true with my oldest, since now he is 21, and he did well in his teens, and understood the consistancy and when mom says no , he knew it would not change , and it really did help through his teens, so hang in there and continue to love both your children evenly, take care and have a good day D. d