In fact, Walt murdered her. He shoved her into a position which caused her death, and then did nothing to stop what he'd set into motion.
Murder implies intent. Walt did not go there with the intent to murder anyone, only to talk to Jesse. I don't think him shaking Jesse (which shook Jane and made her fall onto her back) can possibly be taken as intent to do anything but wake him up. It's criminally negligent homicide at worst, not murder. And it would be a tough case to prove criminally negligent homicide since she never would have thrown up or been too deeply unconscious to save herself had she not been injecting heroin.
Season two is all about the unintended consequences of Walt's decision, culminating in the crash. Jane would not have died if Walt hadn't decided to cook meth. Or at least, she wouldn't have died when and where she did. I just rewatched it recently and was surprised by how much Jane grew on me in retrospect and how rich the season is with layers upon layers of foreshadowing and echoes.