Where Did my sweet girl go?

Living with Layla these days is like living with some one who has bi polar, she is up and down....and driving me crazy! We use to have a sweet girl who listened to us, behaved out in public and slept through the night. Well ALL of that is gone :(
Over the last couple of weeks Layla has spent time in "time out" almost every day. Usually for hitting Jack or Molly. She is very mean to both of our pets, and we will not have her abusing animals. For the most part she doesn't mind time out, and in fact has put her self in time out a few times.
After the first few days of big girl bed the honeymoon was over. Layla will wake up to pee and not go back to sleep, even if its 4 am! We walk her back in over and over again but she just keeps coming out of her room. I should be pleased that is she completely potty trained including at night by 25 months but really I would be fine with her sleeping through the night and using her diaper. But our girl is done with diapers and wants to use the potty, no matter what time of day it is.
Terrible two?? I sure hope so because that means she will not be a brat for ever!