telling my daughter she's adopted...

Ka
My husband and I have been together since I was 6 months pregnant. My daughters biological father signed the birth certificate and then disappeared when she was 7 months old. 
Earlier this week we paid a lawyer to start the adoption process so that my husband can adopt her. He biological father agreed and is going to sign the paperwork. 
I asked our lawyer if our daughter could skip the court date and just have my husband and I go in her place. Our lawyer said that wouldn't look good to the judge, because adoptions are supposed to be a happy thing and she's at an age where they'll want to know that she's happy with this decision. 
My husband is the only father my daughter has ever known. She doesn't even know her real father exists. She has her real dads last name, but since my husband and I just got married, it makes sense to her that because my last name changed hers will too.
I know we'll tell her eventually, but I feel like telling her now will only confuse and crush her. 
What do you ladies think is a good way to tell her what's going on? She'll be 5 tomorrow and I just don't know how to go about it.