Since the child is just 3, I'd eliminate the "half", all she needs to know is that she has a sister. She's waaaay too young to even understand how they are sisters anyway and if she does ask, you simply explain that she (the sister) has a different mommy. Besides so many families are blended now anyway, it's kinda the norm for many. My older half sister always introduced me as her half sister when I was a kid and she would kinda make me mad doing this so I finally started responding when she did this with, what half am I? The left, right, top or bottom. Needless to say, now upon an introduction to someone new, I am her sister.
M. in Camden, MI