H.W.
I don't know that I could say you are doing anything 'wrong', per se. If you do yell, or get upset or emotional (which is a common feeling in this situation), you may have some attention-getting behavior going on, so with all of what I suggest, try to stay as emotionally neutral as possible.
Breaking it down from your list of problem actions/behaviors:
1.Not listening to simple directions: Because of the transitions going on in your house, she will likely respond better to directions by getting some connection with you first. "Connect, then direct." A.If you are asking her to stop something she's doing (say, coloring a picture, for example), I would go and first ask her something about what she's engaged in. "Oh, you used a lot of blue right there. Tell me about that." (open-ended question, connection, she sees you are interested in her, good feeling, validation of her self) Then, when you have the eye contact, say "In just a minute, I'll need you to..." B. If you need to catch her quickly, smile, (connection with good feeling, eyes), "You say it after me: In two minutes, I will go wash my hands for dinner." use a pleasant tone and have her repeat it. If she blanks out.."what's going to happen in two minutes?" and if she doesn't pick up on the cue, give the whole direction to her again. Make sure that after she does what you need, you give her a physical response of your love-- pat her back, squeeze on shoulder, tousle her hair-- and say "Thanks for taking care of that".
2. Questioning you on your directions to her: whenever possible, act completely nonchalant and ask "Oh, why do you think you need to (do task)?" If she gives a correct answer, smile. "You figured it out, kiddo. Go get it done!" This is a great age for 'racing'--can she get her task done before you get your task done? And if she's snotty in her answer, just reply cooly "Oh, I see you need to think about it some more. Go do it and see if you can figure it out."
3. Doing something you've asked her not to do: this is willful disobedience. I would do a time out for this, for five minutes, or if more appropriate, a loss of a privilege connected to what's going on at the time. What I often tell my son when he has time out is to think of other solutions to the problem at hand. For example: "I asked you to leave the fan alone, and you decided to touch it anyway. That's a problem because it's dangerous. I want you to think about what you could do the next time you want to touch the fan." I prefer to focus not so much on the 'you disobeyed me' (which can get them stuck in a power struggle) and instead use their time to come up with some other solutions to doing something they were asked not to do. Then, if she has some answers for you, write them down on paper and put them on the fridge. She'll feel her alternatives to disobeying have merit.
4.Bossing. I either ignore it, or just tell my son calmly:"You know, I've been doing this a long time and I know what I'm doing." If the tone is rude, then "Your voice is so rude, my ears don't want to hear what you are saying." Ignore, then once her voice changes tone, proceed to asserting your calm, motherly authority that you are very capable of doing XYZ, thanks.
If the rudeness goes on for more than a few minutes, can you just put her in her room until YOU are ready for her to come out? When my son (also 5) gets an attitude, I just tell him "I can see by your actions/hear in your voice that you are not ready to listen to me right now. You need to take a break. Go play and I'll come get you when I'm ready to check in with you." I am a firm believer that if more adults knew to go take a break when they were in a snit, the world would be a better place. "It's okay to take a break when you aren't feeling friendly." Then, do the check-in, and don't pontificate-- just "are you ready to be friendly again?" and take it from there.
Lastly, every chance you get--nonverbal, physical affirmation of her self from you and Daddy. When you walk by, squeeze her shoulder, stroke her back, her hair, lots of loving touches that don't take her away from what she's doing. Smile at her when she's busy and looks up at you. This is called Positive Attention during Neutral Times (from Joanne Nordling's book "Taking Charge: Caring Discipline that works at home and at school"). This technique is quantity, not quality, based. Lots of those good touches when she's busy at her own bliss--not doing anything to please you, that is-- is a very powerful tool in helping to affirm the child's place in our hearts, that they are important and matter. This is not the same as being over-indulgent to build up their self-esteem, either, or overpraising... this is really about showing your little girl that she is loved *just* for who she is.
Good luck, Mama! These kiddos can be tough!