J.C.
Mom,
My heart aches for your little one in what she is going through. Be sure that she is seeing plenty of Daddy even in this tough time. Maybe you can start a new bedtime routine with her. A nice bath, some warm milk , get her favorite bedtime toy (teddy or a soft blanket she sleeps with)and get a few new sweet children's bedtime story books at her age level to read to her each night. Be sure you are reinforcing how much you both love her by telling her and giving her plenty of hugs and kisses. If she is verbal and talking in sentences I would also look into seeing a psychologist for some play therapy to help her but find one that is trained to work with young children. If at all possible too please consider marital counseling with your husband if you have not already, divorce is a devastating thing for a child.
Good Luck Mom