Mab eyeballing Lara as a potential replacement makes a lot of sense, especially when you look at the functions of the mantles and why they operate that way. My read on the situation is that the Lady mantle denies it's holder sex as a means of teaching control and responsibility and restraint. Once they have learned to master that then they might be ready to be the next Mab/Titania. But looking at the history and what Jim has said about each of the mantles, the higher you go the less likely there is change (I believe he said Mother Summer has changed once, and Mother Winter has never given up her post). That tracks with what we know of Mab...she's been Mab for a thousand years, and the only Winter Ladies we know of are Maeve and Molly...there obviously were Winter Ladies before Maeve, so the question is whether they were actual daughters of Mab, and more importantly, were they discarded because they showed the same lack of restraint as Maeve? I think the answer to that is a yes, and it also explains why Mab does not want her mantle to pass to Molly yet--she doesn't think she has the necessary control and restraint. Lara then, having managed to gain control over her demon (at least as much as possible) presents an ideal alternative if something should happen to Mab, someone who has demonstrated restraint and control and can operate without passion if necessary.
