4 Year Old behaivor issues

My 4 year old daughter will be 5 in December.  For the first 3 year of her life she was the most angelic child you could imagine.  Went to bed like a dream, very social, well spoken and polite and most of all respected her parents.
and then her little brother arrived and since then her behaivor has gotten worse and worse.  I thought it was a phase - but now I don't know.
She is extremely emotional - if we tell her "no" to something she just goes into a total meltdown of hysterical crying and I have no idea how to react.  We have been telling her "there is no need to be crying" but it's obviously not working.
She also is talking back, not being very nice to her little brother and most of all NOT GOING TO BED.  We have to put her to bed 10 times a night because she keeps getting up and she purposely speaks loudly so she'll wake up her little brother.
I am at my wits end with her, I just don't know what to do.

[Kevin Kennedy, Ph.D.]

While from your point of view there may be no need to cry, that really does not resonate with your daughter. Rather than focus on the crying or upset, keep your attention focused on the rules of the household. If your daughter is violating the rules, use sound discipline and limit-setting, such as the plan detailed in Lynn Clark's book SOS Help for Parents (see www.sosprograms.com). Remember that her world was turned upside down with the arrival of her sibling. This causes a major adjustment for young children.