So Lillith’s plan from the start was to make Sam strong enough to kill her and break the last seal. I don’t understand the episode where she tried to seduce Sam into killing himself and Dean in exchange for her retreat. What was her purpose? Was she simply testing to see how strong he was? Trying to fool him into thinking she was getting desperate?
It was probably either a test or it was part of Sam’s conditioning as a vessel(dunno when they reveal this) or maybe she just wanted a close look at the most important two humans in existence or something. BTW it wasn’t really Lilith’s plan, she was just following orders.
EDIT:Remember that beating Lilith was the reason for a lot of things that they needed to happen to Sam, from him drinking massive amounts of demon blood to developing his mental powers, she was just a slippery slope trap from day one.
It’s been a while since I’ve seen it, but my recollection is that she had at least a moment or two of wanting to scrap the whole plan to save her own skin. Does that make sense?