Will she be getting a trait when you age her up? If so, I suggest you don't, you may get a trait you don't want her to have.
My first sim family I thought they had to have a cake to age up. Unfortunately, he didn't eat any of it, but mom and dad ate some and they aged up to elders. I bought another cake and he aged up, but since he hadn't gone through the stage, he was given a trait by the progaming, a negative one.
If she is going from to toddler to child, you lose a chance to pick a trait. Someone correct me if I am wrong; birth you get to chose two traits; baby to toddler no trait is given; toddler to child you pick a trait; from child to teen I am pretty sure you pick a trait; and from teen to young adult, I don't know. These all depend on how good a parent you are.
My baby that was born in a family yesterday, it was so hectic that I guess I goofed somewhere. I was allowed to pick only one trait which was a first for me. He was given the trait of genius.