Is it bad I'm this honest with my child?

My 8, almost 9 year old daughter has been difficult to handle since she was very little. She has had lots of behavioral problems as well as a lot of poop/pee accidents, still to this day. She does weird things like hawking up a loogie on her hands and rubbing it on things. She lies constantly, even about the smallest things and she doesn't seem to care about how anything she does affects anyone but herself.

Today, I had a candle going and she rubbed her fingers on the inside of the candle and got black all over her fingers and decided to rub it all over the toilet seat. When I asked her about it ( I know she did it because I had just cleaned the bathroom and she was the only one there since I cleaned) She lied and said 3 different things. 1.) I didn't do it, 2.) I did it yesterday and 3.) I don't remember doing it. She said all 3 things one after the other. I sent her to her room because I was furious she was lying to me again.

After calming down I went in to talk to her and asked one more time if she did it and not to lie because I already know the truth. She finally said yes she did it but when I asked why she did it she said she didn't know. (Her normal response when I ask why she's doing something)

I told her I'm more mad about the lying than what she did and that when dad gets home she will be in trouble. Her response was "so will I not get a prize tonight?" (Apparently my husband said she would get a prize if she did really good today) I was frustrated that was all she was worried about and said "Why is that the only thing you care about? Why are you only concerned about what you are going to get or not going to get? You don't care about what you did, you are only upset you got caught and you don't seem to care about what you do or say or how it affects other people. You have no remorse and you need to stay in your room and think about that for a while."

Was I too harsh? I feel bad but at the same time I feel like it needs to be said because any punishment that is given, she doesn't seem to care about. She does a lot of other things like hurting her 3 year old brother and she only cares that she is in trouble but doesn't seem to care that he got hurt.