from princess to pirate...back to princess

I was reading up on the emotional development from age 4 1/2 to 5 the other day, and found something out that I had suspected. My little princess can turn into a pirate at will. In the past few weeks, Ingrid has started growling, grunting, chasing, terrorizing Ilsa, and hiding around corners to scare the snot out of us. On one hand I'm excited that she is exploring beyond pink hearts, flowers and crowns, but along with this exploration of aggression, she has also developed a bad temper. This has been an issue at times.

Much of the day is spent bossing Ilsa around at the top of her lungs, thusly (I have always wanted to use that word):

Ingrid: "Ilsa, give that to me!"
Ilsa: "No, I want it."
Ingrid: "NOW!"
Ilsa: "Wahhhhhh"
Ingrid: "GRRRRRRR!!!!!!!"
Mommy: "Ingrid, treat your sister with kindness and gentleness. Ask again."
Ingrid: "NO! I WANT IT NOOOOOOWWWWW"
Mommy: "Discipline time...."

This isn't going to be a discipline rant. So bear with me, it gets funnier. Yesterday, I was washing the car. (Ahhhh, Christmas in Almost Mexico...I wore shorts and Chaco's.) She got bored with helping me, so she decided to create a fort in the garage (that's cool) from umbrellas. She used two little ones and one huge obnoxious blue and white diamond design golf umbrella from Munich. She added in the just-washed floor mats to seal up the cracks between the umbrellas. Then she announced, "I need priiiivacy." Here's the exchange:

Ilsa: "Can I come in Ingwid?" (in the sweetest, cutest high little smiley Ilsa voice possible.)
Ingrid: "NO! I neeeed priiiivacy! Just give me TWO MINUTES! That's all I need. Now go away!!!" (ok, I take credit dubiously for the two minutes crack)
Ilsa: "But IIIIII want to be with Ingwiiiid." (half whimpering)
Ingrid: "Aaaaaaaaaaaarrrrggggghhhhhhhh!" (pirate voice)

And as suddenly as the pirate emerged, the sweet princess will re-appear, though not as often. Usually the sweet, gentle, quiet, timid Ingrid shows herself at pre-k, when she doesn't want me to leave. The other night I wanted to go to the gym to work out. She sobbed at the learning that I was going to leave (10 minutes before her bedtime). I stayed and comforted her for a while, and within minutes she was back to herself.

Is this split personality normal for almost 5 year olds? I want to know. Tell me! When is it going to end!