Much like baby mama. Except, when used by the grandmother in the situation the baby mama would be called her "grandbaby mama".
For example:
My friend said her son and his girlfriend are having a baby. The girlfriend is going to be her grandbaby mama.
Instead of having baby mama drama, you may have grandbaby mama drama.
My friend said her son and his girlfriend are having a baby. The girlfriend is going to be her grandbaby mama.
Instead of having baby mama drama, you may have grandbaby mama drama.
by A friend of Grandbaby Mama January 2, 2010