Your daughter needs to know that you understand her anger, that she's entitled to her anger-- that she CAN express it, but that there are appropriate ways and inappropriate ways to do that.
But first, she needs to know that you understand and have compassion for her feelings. Seeing everything from HER perspective and helping her to know that you really do understand will help her to feel validated which will hopefully result in her not feeling the need to rebel so much.
So let's look at this through her eyes:
You said that the husband that you're now separated from was your daughter's stepfather?? So if I read that right, this little girl already lost one father, now she's losing another. (I understand that he's still involved, but "visiting" dad isn't the same thing as living in the same home and having that security)
In 5 years, she's lost two fathers, and on top of that she's separated from you alot because of work. She has no security. That's an awful lot of chaos and instability for such a young child to handle. And what you're seeing is evidence that she's NOT handling it. And really, how can she? That's alot for even an adult to cope with, so how can anyone expect a 5 year old to cope with it? I'm sure you and your husband have your reasons for the divorce-- but no matter how legitimate those reasons may be, your daughter isn't old enough to understand or even care. All she knows or understands is that Daddy's gone and that her family and security have been torn apart and everyone ELSE is making decisions that she doesn't like. She has NO power or control of all the horrible things that are happening. And in fact, it's the people she loves and who love HER who are "doing this to her"-- and she's angry about it. She CAN'T say no to the divorce-- she's has no control over that. Mom and Dad are going to break up, no matter how she feels about it. But she CAN say no to putting her back pack away. She can refuse to get dressed, to clean up her mess, etc. She has control over that. See what I mean? So she's taking it where she can get it. It's her way to express her anger, and really, a way to get even. "You hurt me, so I'm going to hurt you". Of course, it's all subconscious for her. She doesn't have the cognitive abilities to even understand what she's doing.
She doesn't have the verbal ability yet to express all that. She doesn't know how to put all her anger and frustration into words the way an adult can. Heck-- even we adults have a hard time finding the right words sometimes. So talking about it with her and helping her to express it verbally can help to lessen her need to express it through misbehavior.
Give her things to do that ARE appropriate ways to express her anger. She could draw a picture, talk to you, scream into a pillow, etc.
The important thing is for her to understand that she has every right to be angry, and that it's okay for her to be angry. She's entitled to those feelings. She just needs to learn how to express it in healthy ways, rather than through defiance and rebellion.