What I think is happening with Dolores is that 30 years ago, she asked for William’s help in tracking down this town so she could reclaim the lost memories of the massacre, but she failed.
Present-Day Dolores is using her memories of William to retrace her journey. This would explain why in some scenes William appears in the shot and then mysteriously vanishes. Her past memories are phasing in and out of her present time frame and she is never certain which time period she is in.