Single Parenting Support Group
Today being raised by a single parent is not uncommon. About three in ten children live in a single parent home. The most common type of single parent home is one with only a mother. However, single father homes are the fastest growing type of family situation; 60% growth in the last ten years alone.
Therapist also said to constantly reassure her. Even though her dad won't be with you and you'll be getting a new house, she'll still have a home (2 homes, in fact if she will have visitation with her father) and she'll keep all of her toys, etc. She can't hear enough that she is loved by everyone. Involve her in decorating her new room. Maybe get her excited about the move.
The questions will get tougher as they get older so be prepared, but always keep it simple and light. Kids usually figure the rest out themselves (or so some of my friends tell me).
Hope that helps.