I don't think we're supposed to see her as traumatized forever; I think the business with the burning hands and telling Spike she loved him was supposed to signify, among other things, that his willing sacrifice healed the scars from Angel's unwilling one. Presumably we're supposed to assume Buffy goes on to have fat grandchildren with a nice insurance salesman, or a glamorous fling with the Immortal, or both. Unfortunately I was so detached from Buffy by the end of the show that her prospects of future happiness with characters I don't know or care about was less than satisfying.