This question already has an answer here:
I am running QGIS 2.18.13 with Grass 7.2.2[1? ... can't remember which number was shown ... see comments below] installed via the OSGEO4W installer on both Windows 7 and Windows 10 (64bit).
(I have double checked within the OSGEO4W "advanced install" directory that the "qgis-grass-plugin7" and qgis-grass-plugin-common" are installed as for version 2.18.13-1)
The Grass Plugin/Toolbox is no longer in the Plugins Manager.
This plugin/toolbox was very handily available in recent versions but seems to have vanished though I am not sure with which update.
Is the plugin/toolbox still available?
How do I re enable it?