Basically, I think Cooper messed up the timeline and I think mother interceded out of self-preservation. That is, Laura exists as a counter-measure to evil, so maybe she can't destroy her, but can fuck with Cooper's plan to prevent her death.
Taken from Reddit: "last scene was a dream laura in 1989 is the dreamer cooper asks what year is it laura's mother calls out to her from the waking world laura recognizes her mother's voice and realize she's dreaming she screams and wakes up back in 1989 the morning they would have found her body had cooper not had changed the past"
Part 17 absolutely phenomenal. I loved the ending to Part 18 but it definitely took a while to get there. Couple of things I noticed: - The pylons that surround Cooper and Diane at 430 miles look a lot like the symbol on Mr C's playing card & Hawk's map - Diane and Coop sex scene instantly reminded me of the scene in the first episode before the glass box massacre. I only wanted another series if Lynch & Frost had vision for one. Looks like they did therefore I'm on board. It really really felt like Part 17 was the end to the series and Part 18 was an epilogue of sorts, to me anyway..
Remember when BOB was thwarted via a random British kid with a giant green hulk hand? Good times. Harry not getting out of his chair the whole office scene was amazing. Lucy shooting Mr. C. was amazing. I think Part 18 is a metaphor for people expecting the show to be the same after a 25 year gap.
Sleeping on it (and by sleeping on it I mean periodically waking up at points during the night and just thinking about different moments and theories), I loved the finale.
The moral of the story, it seems to me, is very dark. This is a series in which the instigating factor was rape, incest, murder and a generalized violence against women. This new series had the same theme. This will persist, even in spite of the actions of good people. We can try to ameliorate it, and we should do so, but it remains a part of the architecture of this universe and cannot be abridged. The effort and journey will always yield partial victories.
I'm all over the internet right now trying to make sense of this. I guess at some point I'm going to read Frost's books then do a rewatch.