[quote=thewizardguy]
She didn't. She had to become the alpha, which required her to defeat the other swarm. The zerg are a hive mind, which will join any 'queen' that can control them, Kerrigan was bullyng them into becoming a part of her army.
[/quote]

the first mission had her control them by psionically linking with the hive.... it's the one where she was in a sealed test chamber....