I use mobilesheets on the Samsung Chromebook Pro as well. I'm not really sure what you are trying to do, but you can fix the orientation on the Chromebook in the settings.
If you have flipped the display all the way (i.e. tablet mode), you can lock the orientation in the quick setting menu by pressing the lower right corner and disable auto rotate . This will only work in tablet mode.
If you are in laptop mode this option is now moved to the general settings under Device->displays->Internal display. Here you can fix orientation to 90 or 270 to keep it in portrait .This works with mobile sheets, and it stays in this orientation regardless of how you turn the device afterwards. I think this is what you are looking for .
If you have flipped the display all the way (i.e. tablet mode), you can lock the orientation in the quick setting menu by pressing the lower right corner and disable auto rotate . This will only work in tablet mode.
If you are in laptop mode this option is now moved to the general settings under Device->displays->Internal display. Here you can fix orientation to 90 or 270 to keep it in portrait .This works with mobile sheets, and it stays in this orientation regardless of how you turn the device afterwards. I think this is what you are looking for .