I think you guys did nail it. I looked up some of the original cover art and it seems to fit. Thanks! Wanted to suggest to a friend's daughter

It really sounds like the Dicey books. They flashback to living in a shack with their mother before she abandons them. Then after they move in with the grandmother she becomes friends with 1 boy and 1 girl at school. There is also a book written from each if the friends' points of view. The boy friend also has a pretty tough home life.

Maybe. Pretty sure I did read the series mentioned. I remember more of the story of her being at home and her friendship with a boy in her school (maybe that was more in Dicey's Song)

Homecoming dicey was 13 and lived on cape cod, I think. She had three younger siblings

Homecoming by Cynthia Voigt? Its sequel is Dicey's Song.

I read a book when I was around 9-12 years old around 1984-1986, it may have been a trilogy. It was about a young white girl around 9-13 years old, very poor like not having shoes for school poor, at one point she stole shoes or found some in a dumpster, think around 1970's in the US east coast (NC or SC maybe), she lived in a shack on a beach (I remember her talking about a sand not dirt floor), she was friends with one boy at school. I think one parent was around but drank too much. It may have won a literary award.
You guys are great at this, any ideas?