When you make a change in one worksheet it happens and is remembered at the worksheet level, what you see on the dashboard is simply a view of the worksheets you're using, thus the current sheets (with their design & organisation). Meaning that in your case you would need to duplicate this sheet in order to have a the same bar chart vertically in one dashboard and horizontally in another the one.
thanks thats what i thought. What about the other way though - make the change in view on the dashboard so it doesnt link back to the worksheet?
That's what I tried to explain. You can't, a dashboard is an addition of worksheet. If you're using the same worksheet in several dashboards it's always going to be the same design. When you reverse the bar chart of your worksheet in your dashboard, it's the worksheet itself your're reversing (the button on the dashboard is simply a shortcut Tableau create to avoid having to jump back in the worksheet to make that change).