It was her objective.

The company was developing "cyborgs" to be weapons. That team proposed and were accepted to develop one that would be more autonomous and similar to humans, they succeeded in developing it and started raising it as parents and friends raising a child. But L-9 was based on previous versions and was still directed into being a weapon. With the disadvantage of not following orders and her emotions making her unpredictable and unable to control her own actions. So, she failed to be able to feel empathy for (other?) humans, failed to get any advantage from her emotions and failed for not following orders.

She turned back into being a living weapon. The doctor believed in her and trusted she'd act as human and hoped she'd pass on his test, but of course she lost control again. The biggest issue was when he told her they're not her friends because friends wouldn't lock her, that made her very angry and she decided to kill them all before they'd lock and kill her.