I am at my wit ends with DD

[Storyofalion]

Sorry, I cant cope with my 4 year old dd anymore, I hate feeling like this about her but I cant help it !!!!!!
She was the sweetest little thing and an only child then her baby sister came last year and everything fell apart .
She will be 5 soon.
I dont know where did I go wrong. We always tried to make sure that she is not going to be a brat , taught her how to be kind and polite, respect others and be thoughtfull , it seems that she is only horrible to me and dh, she can be horrible to her sister too, apparently there are no issues with her in school and there weren't any at preschool.

I thought it was jealousy at first but I always try to spend as much time as possible with her, we do fun things together, have walks and do one to one trips.
She is ALWAYS unhappy, no matter what we do she wont like it, she screams, acts like a brat, wants life to go her own way without thinking of others.
I am such a failure , I look at other well behaved children and feel jelous :(
I read books about children development and look for ways to improve myself but I still cant find the issue, what am I doing wrong ?
I always wanted children and I love them so much, I dont know if she even likes me :(

I try to teach her about the consequences of bad behaviour , we have stickers charts BUT nothing really works,

She screams every 30 minutes when home, wants every toy or sweets from shops and is never satisfied with anything shes getting.
We stopped buying her toys or snacks but it didnt make any change .

She screams when I ask her to tidy up toys
She screams when asked to brush her teeth ( despite doing it three times since baby)
She screams when asked to eat breakfast
She screams when asked to dress herself

When she screams/cries I usually askn her if she needs to cuddle and try to explain calmly and make her feel safe.

It doesnt stop, her behaviour isnt improving and I need some advices as I dont want to ruin her life or make the same mistakes with my younger one :(((

I know people in the past were punishing kids but this is not what I am looking for in parenting.
Is this where I went wrong ?

My life is a chaos now . I need help as I cant cope with her screams and being this way any more.

I am very calm myself but I dont want to loose the shit one day.

"When she screams/cries I usually ask her if she needs to cuddle and try to explain calmly and make her feel safe."

And is that helping? Have you tried to ignore her tantrums and demands? Unless she is ill or injured, it would do no harm to take absolutely no notice of her screaming (difficult to do) and to put her on the naughty step/in another room. That type of behaviour needs to be addressed properly, and cajoling her clearly is the wrong course of action. She has got you exactly where she wants you - dancing to her tune. Have a look at SuperNanny on youTube

Get yourself a copy of 'How to talk so kids will listen and listen do kids will talk.'

What a load of tosh. This is a 4year old child who was beautifully behaved until a younger sibling came along. The child is struggling.

OP do you honestly mean your daughter is always unhappy? I think, if she's that bad, you need to seek outside help. If there are good and bad spells, what precedes the good and triggers the bad? How well does she eat, sleep? Has she settled at school? A lot of children are very unsettled and badly behaved in the run up to beginning school. Do you have good routines, does she know what to expect from the day? Is her physical health good, any problems with allergies, eczema, eyesight, ears?