@JavelinJoe
Most thoughtforms (Demons, Angels, Devils, Gods, forces of nature) are neigh-immortal. For Lilyn, she's a succubus with various "Conditions" of immortality. One of them is draining life from other sources.
She must of refined the technique to use the life drained so that she doesn't starve herself or burn herself out. But the 2nd condition is Parenthood. The energy she uses is recycled to help her children grow.