The Deep Mother seems to be the symbol of all the things in the ocean, or the ocean itself. Little is known about this symbol of murloc religion.
In murloc society, murloc shamans commune with the water (the Deep Mother) and her favored children, and handle the tribe's rituals.
As with all murlocs, the White Shark tribe is religious. They worship the Deep Mother, the water, and her favored children.
There is a slim possibility that due to it's symbolic nature concerning water in the depths, the Deep Mother could very well be the Empress of Nazjatar herself. This of course is just speculation.