in episode 4, after returning from the funeral of owen's mother (who died of alzheimer) jamie says that she would rather die than "being worn away a little bit every day" and this is basically what happens with dani.

in the last episode, we see dani staring at her reflection in the bathtub and she says that every day she feels like she's fading away and that she can't feel anything anymore (this is also an allusion to depression).

the next scene is the one where she almost chokes jamie while she's sleeping. she's not herself anymore, viola is taking control of her life and she cannot put jamie at risk. so she goes back to the lake +

and she loses all her memories. she will not remember her life with jamie and all the wonderful years they spent together, but she will stay alive in the memories of the woman who loved her the most. because jamie kept her promise: she felt everything for both of them.