Because Opal's mom left her when she was very young, Opal doesn't know too much about her mother--though she longs to. At its heart, this novel is a story about learning to let go. But in order to let go of the longing for her mother, Opal has to learn more about her first.
She finally does in Chapter 4, when her father tells Opal ten things about her mother.
The most important of these is that Opal's mother loved Opal very much.
We also find out about the mom's physical appearance ("red hair and freckles") and her talents for growing plants and running fast.
We know that she was unhappy being a preacher's wife, and that, sadly, she was an alcoholic.
But she was also funny and loved to hear a good, funny story.
Most interesting of all was that Opal's mom was fascinated by the constellations in the night sky. She knew all about them and could point them out one by one.
Because this is all that we (and Opal) know about her mother, we can only conclude that she was a deeply troubled person who nevertheless found joy in life and who loved her daughter dearly.