I'm going to offer you a different interpretation that involves a closer reading of the elements in your dream and a different psychological principle or two from the comments you have received already. I hope this will contribute further to the value of you're receiving from this website. And I still want you to pay whomever you wish--because competing for your cash is not my purpose, but helping you to benefit more from the lengthy grieving process you've already given to your loss.
Folk wisdom has it that a mother never can outgrow her sorrow over losing a child. But Carl Gustav Jung's approach to dream interpretation holds out the promise that the Higher Power (aka God) that conceives and presents our dreams uses their precise details to guide us toward further development of our own personalities, often by offering up some spiritual aspects of the dearly beloved and of our response to them for our own higher education in the developments of our human encounter with the Divine within and around us.
I don't know how you feel now, when awake, about your daughter's unwillingness to come back to you before her death--and I'd be interested to know if it's any different than what your dream appears to reflect: For it is normal for a grieving person to feel guilty about something she did or did not say or do toward the deceased person, and to experience in a dream the emotional & symbolic resolution and relief from her guilt, sometimes even 18 months after her loss. And it's normally quite a while later that the grieving person may get around to being angry at the deceased for Leaving Her alone under circumstances over which she had no chance of control.
But your dream begins with a version of the Second Scene I've described above, which therefore serves as the exposition-theme or "Problem Statement" that the remainder of the dream proceeds to elaborate and explore in search of resolution, meaning and growth. I'm guessing that you had already felt angry many times that your daughter would not come back home to you and try WITH you to resolve her problems -- that seem to me to be related to relationships or addiction. Please correct me with what actually happened if you're willing.
The next scene would be, in dream psycho-logic, a consequence of the first scene: "she backed up into an elevator . . . really sobbing." This is her symbolic reaction to your anger that she "did what she did"--WHAT did she do? AND "didn't just come home." I can't comment or interpret the first (prior to the dream) cause of your anger. But the second cause--not coming home--Might have different shades of meaning, depending on 1. her age, 2. her intrinsic goals in her life, whether your or she understood them or not, 3. her own personality in comparison & contrast to yours, and 4. the historical traditions of your family concerning the life trajectories of women, to leave their families and/or adopt different goals and behavior patterns than other family women.
From your dream it appears that she left you by living even before she left you by dying. Was your anger about that action of hers communicated in real life even before it occurs in this dream? Was your anger so well known that it was a (psychological) "fact of life" in your ongoing relationship?
I ask this in all seriousness, because the immediate consequences produce the symbolic climax of your dream: "she BACKED UP into an elevator." Backing up is very meaningful as a pantomime: She RETREATS by going backward, while facing you warily, that is ready to defend herself against any further advances from you. (Does this describe a recurrent, perhaps unconscious-to-you, relational dance between the two of you?)
Backing up is both a physically defensive retreating-from (you or the family you may represent, and possibly a symbolic motion suggesting regressive retreat from adulthood into adolescence or even childhood.
Now an ELEVATOR is a really interesting symbol: It's a means of rapidly going both UP and DOWN. In terms of addictions an elevator could be getting high or getting low; as "mood elevators" go, it simulates bipolar behavior. Was your expectation in the dream that this elevator was about to go up, or down, or either way unexpectedly?
Next scene: She lowers herself in front of you feeling utterly defeated--you're standing she's sitting beneath you. And her mouth was "sowing shut." So something inside of her was progressively sowing her mouth shut--preventing her from speaking.
My GUESS is that she's unable AND unwilling to speak HER own truth, and perhaps can't even THINK UP what it is. Because whatever that might be cannot have any meaning for you (or her whole family) because it does not fit into the woven-together meanings of all personal and social realities belonging to you and your family as You-All know them. This kind of "struck-dumb-ness" often occurs in family members or outliers in any human group who sense that what they perceive, think and care about will meet with no interest or undrstanding from those around them. SO SHE HAS LOST HER "VOICE."
as the doors of her separating prison/cage (addiction-solitarylifestyle) are shutting (simultaneously with the voice of her inner truth--your eyes meet: and this symbolizes a moment of mutual conscious awareness of each other. Awareness that you have LOST your chance to share intimacies, because you can't speak the same language, so can't make yourselves understood. Your dream-ego character (that part of your whole self that the Dream Director wants you to reflect on most in this scene) sees that she was trying to say "sorry"--Was that because THAT's a word you would understand, and perhaps expect AND welcome? Along with "I love you mum?"
That's the final scene as the doors closed. But the communication you have wanted HAS BEGUN. And you can continue it, by writing letters to her, perhaps by trying to draw her out about the realities of her life and her inner dialogues. And thus you might trigger more dreams that you can also write down and send in.