Dear J.,
I cannot speak to the step-child issue BUT I can speak to the "4 year old whining". Both my son and daughter went through similar issues as you said at 4. I infact feel that 4 years is much worse than 2 years. Both had baby talk, tantrums, whining, and the beginning of "an attitude". With my children I found a combination of things worked: ignore the small annoying behaviors, we would say we did not understand them when they spoke like a baby and asked them to talk like a big 4 year old, tantrums we continued to ignore and told them they will never get what they want when they throw a tantrum (if a tantrum became destructive or a huge disturbance -we removed them to the safety of their room and any resulting destruction they would be responsible for cleaning-up and returning to an orderly state. If they ask kindly for my help, I would help clean), I remind them of all the things a big 4 year old can do that a baby cannot (swing, bike ride, eat ice cream, have chocolate, stay-up later, play games), and I would encourage and applaud good choices with words, play, stories, treats, and verbal praise with hugs.
4 was also when my children both started choosing one parent over another and then switching this clinginess after a week or so (and yes, I found it hard not to be emotionally hurt as did my spouse). Also, in my humble opinion, by 2 years of age I believe most children start learning the "art of manipulation" and All children become demanding. It is their nature to be demanding as most things they still cannot do for themselves (food, bathing, going somewhere) so this translates to them demanding EVERYTHING! I try to begin the teaching of kind words & actions to achieve what you want. Also ask for something directly, don't whine & don't manipulate. My good friend would reward her children (and I learned to say it as well) by saying, "when you make good choices, good things happen".
It is hard; hard not to be emotionally hurt, hard not to loose your patience, hard not to get resentful. For a big part of 4 years old I did not like my daughter- I always love her and tell her so all the time but I did not like her behavior. But I am happy to say it passes. And I don't know why but my now 4 yr old son does not seem to have these issues AS bad- there still happening but not to the level of my daughter. I also know I am harder on my daughter and try to be aware of this when I view her behavior and sometimes I know I need to back-off a bit and give her space and not view her under a microscope all the time.
Don't give-up if it means enough to you BUT do communicate with your boyfriend about your feelings and what he expects of you and what you need from him as support (your step-daughter's respect, kindness, etc.). Even though she is not yours biologically, you are her father's partner and deserve the same respect and kindness you show her when she is in your home.
It does get better and she can learn that her behavior directly relates to her getting the things she wants sometimes and the things she needs all the time.
Fondly,
ann m.