You can watch video on-demand (VOD)/non-linear programming on their site (meaning, stream full episodes/movies). The option to view a live stream of what is currently airing on the channel is not available. (This applies not only to Lifetime, but all A+E channels, like A&E, History, and fyi,.)
As stated in the TVE FAQ/announcement post, A+E owned channels are not supported by Channels' TVE implementation.