I wonder if Maura had a one night stand with some guy at a party and got pregnant? I can see that causing her world to go upside down. How could she explain that to her BF? She would have been in a terrible dilemma, if she loved and wanted to marry Bill. To me, it explains her highly emotional reactions and actions after crashing her dad's car.
I may be way off base here, but this scenario seems plausible. However, it doesn't explain what happened to her after her crash in NH.
Yes no matter what her reason for her being there the wreck changed things. There are only so many scenarios, she was abducted, she succumbed to the elements, the wreck somehow made her see things differently and decided to have her child and is living somewhere. I know the last one isn't likely, but it's a nice thought. There is always something else we may not have thought too. I have found it hard to believe that she ran into a serial killer on such a dark cold night. Also if she was pregnant I'm sure she would have let that be known to her killer which would have made this guy even more of a monster. There also could have been some type of accident and someone could have panicked and hid her body.