7 year old daughter

Can you make sense out of a situation where a 7 year old girl would say hurtful things to her mother (i.e. I feel like I wish you weren't here or I feel like I hate you) for no apparent reason? She will say things like this out of the blue when there has been no arguing.

Children test limits, in order to learn what happens, when they say or do certain things.

Read about learning to say no.

Read more about children's acting out.

Do you feel that I should have my daughter talk to a professional for such behavior? I would understand this behavior if things were being said to me in the heat of anger. However, that is not the case here. I could just be doing something as simple as fixing her hair when she'll say mean things to me. I thought that maybe she was doing all of this for attention. She is the oldest of my four children and my only daughter. I thought that maybe she felt that I was giving her brothers more attention than her or maybe she felt that she was being left out in some way. If this is the case, I can't understand her feelings because she is probably the child that gets to do the most things being that she is the oldest. I've tried talking to her and she tells me that she doesn't know why these things "pop" in her head. It doesn't seem to disrupt her life in any way other than her disrespect for me by saying these mean things gets her in trouble. As far as I know, I am the only one that she is being like this towards. She will only say these things to me when we are alone or when she can whisper them to me. She does say mean things about her 5 year old brother to me as well like, "I feel like I like everybody else on his baseball team better than him" or " I feel like he is ugly." My 5 year old boy is a true "mama's boy" and is very loving toward me. So, I thought maybe there was some jealousy there which would explain the reason for why she would only be this way towards he and I. What I can't understand is why now. Things have not changed between any of us other than my baby being born in the summer last year, but even that has been 9 months ago now. I would appreciate your thoughts or suggestions in how to remedy this problem and how I should react to it.