Hi Allie,
I just wanted to say I think you did a very good job of explaining it to her. Honesty is best, kids are so smart and they deserve the truth. Very good job.
I was wondering if making a sort of memory daddy- day might help. Pick a day with her, and watch any video tape you may have of him, make a collage, photo- type poster, maybe talk about his favorite things, make his favorite meal. You could even bake a cake for 'daddy', and do all these things with her. You could even say, now we'll have our own new "holiday" each year, and we'll do this again next year.
To a child this might seem like the special time of the the year she get's to see Daddy.
I'm saying this b/c it seems like most little kids that lose a parent feel an intense lack of control, and if you let her do these things with her, she would feel like she was a part of it. It's also creating a positive memory for you both together, and strengthening your bond.
My thoughts and prayers are with you, both.
Christian