DD 3 years and 8 months. Always been a handful but the last 8 months have been a lot easier. Felt we had got somewhere 
DS is 16 months, much easier. Easy baby, very active but happy toddler until recently.
In the last few weeks it seems to have fallen apart.
DS and DD both waking at night, occassionally.
I'm full of cold, they have had a cold.
DD has been awful. In the last week she has regressed to being like a 2 year old. Lying on floors, screaming/shouting/kicking and utterly out of control.
She is fine at nursery (2 days a week) and only like this with me if DS is around.
Until now I would say shes been very good with him. He has become more demanding emotionally and has gone from loving her in dedication to wanting me, and its become a bit of a fight for my attention (which DD wasn't previously that interested in)
DS naps 2 hours ecah lunch so DD and I have that time by ourselves. The problems start when we get him up, she just switches.
Today she has pushed him several times, taken things off him and said spiteful things to him. Hes starting to undestand more, so in turn he runs to me crying, which makes her hysterical (literally)
Today I feel guilty because she pushed it and pushed it and pushed it, I warned her calmly several times to leave him alone (everything he had she wanted, and there were some things (of his) that I wouldnt let her take off him). She grabbed them, he screamed. I asked her several times to give them back and she screamed "NO" in my face and pushed me (I was sitting) and I pushed her back
she fell to the floor and then cried.
I feel awful and I know it wasnt a controlled reaction, not pleased with myself. I didnt even push hard but anyway she fell (on to carpet). She carried on with her defiance and shouting but I felt too guilty to do a lot else. She has gone to bed earlier than usual but I am worried at how angry she has made me this last week. I dont get cross with DS, hes a baby and not pushing the same buttons. I love her and need a calm solution to her behaviour please, time out doesnt work for her, she doesnt calm down.