The best thing to do with grief is to go with the flow. That's really all you
can do..
I would think, from what you say, that you don't really know what you missed out on, and so that adds to the grief. Except that you may well have buried that, because its been too painful to bear, but that has come out in the SI and depression.
except that i missed out on something special.
seems pretty key. The maternal relationship is your first attachment, and from that you develop as a person.
I never lost my mother in the way you have, but I was separated from her at birth whilst I was in an incubator, and didn't have any contact with her until I was 3 weeks old, and was in hospital 2 months. That has had a deep impact on my life, leading me to feel unable to truly connect with people a lot of the time, and I have a lot of grief and sadness connected with that.
Maybe one way to start is by trying to connect with you when you were 6 years old. Looking at some old photos. Having an internal or written dialogue with 6 year old you. Letting 6 year old you draw how she felt.. that kind of thing.