i have kinda the same problem! my daughter is 3 1/2 and my son is turning one on saturday. she didn't start misbehaving until he started moving, crawiling and walking. i know exactly what you are going thru. i know the one thing that my daughter hates is when i put her upstairs in her room, on her bed for a timeout. she had never slept in her own bed, bad decision, but i think that is why she hates it. the worst part is now her little brother sees her doing it and he throws worse tantrums than she does! i think it is normal for them to do that, i would just start to reward for the good behavior, praise good behavior, and try something that is effective when she is not behaving. my daughter is normally only in her room for about 5 minutes and she is 100% better when she comes out. i think making her be by herself makes her realize that if she is being bad then that is what is going to happen. kinda long and a little confusing but i hope this helps!