originally posted by Alex_D
She is going to become the queen of blades again, but this time her mind is intact and she will still be "normal" Kerrigan.
This is what it said on the Starcraft 2 wiki for Heart of the Swarm campaign features.
"The campaign is focused on Kerrigan and the development of a zerg empire. The campaign operates similarly to an RPG, in which Kerrigan is focused on increasing her personal power through mutations."
As you can see here, Kerrigan will be mutating back to the Queen of Blades to increase her power, aka leveling up.
"Zerg armies protect her as she garners this power. The greater her power, the more zerg she's able to control."
As you can see here, she will be having to mutate back into the Queen of Blades to control more of the zerg units. Something like Wings of Liberty's unit unlock system.
"Like Wings of Liberty, the player will be presented with choices as to which missions to carry out and which units to get, but such choices won't be based on cash."
Similar to WoL and you can choose etc...
"Both the missions and their objectives are intended to be quite different from the ones featured in Wings of Liberty."
All backed up by blizzard sources.
So as you can see, Kerrigan will have to turn back into "infested" Kerrigan to gain full control of all the zerg units again.
So I'm guessing with her hair still in place, the first few units she can control are drones, larvas and most likely hydralisk/zerglings. Then you can unlock more of the other units as you progress in the story.
Sounds like it is going to be a really good game to me.