I'm sorry for your loss and your current circumstance. I can relate to that emotion of wishing you had a proper goodbye, wishing you could have treated them better while they were still alive, wishing you had known so you could have prepared in some sort of way.
Let me tell you, there is no proper goodbye and there is no proper preparation. There is no true closure to grief, the only proper goodbye there is, is celebrating the life and memories of the person who still lives on in your heart. It is truly a sad thing, and I am sorry you did not have the opportunity to say your goodbyes. I am sure, if she knew who you were today and what you have accomplished so far she would be proud. Everything you have done is not pointless, it is a representation of the good you have done. The good that she saw and loved in you and what the world also appreciates.
I hope you appreciate and love yourself too, do not punish yourself and do not feel guilty for being inadequate in your ways. It is not your fault and I am sure the joy and precious moments you shared gave her great joy during her lifetime, that is all we can hope in our lifetime as humans.
These dreams seem to almost be haunting, as if your subconscious thoughts and emotions are resurfacing. Perhaps, these are emotions you have not being able to process properly and are probably translating in your dreams. I think accepting your emotions, your feelings, forgiving yourself and forgiving the situation will help you heal this grief and pain of yours. Perhaps writing, confiding to a friend, or a counsellor about your emotions will help you process and heal these current emotions.
All the best,