I suspect Barah to be a farm name rather than a hamlet; it wasn't large enough in 1851 to make it into Kain, R.J.P. & Oliver, R.R. (2001). Historic Parishes of England and Wales : an Electronic Map of Boundaries before 1850 with a Gazetteer and Metadata. [data collection]. (Unfortunately I only have the Gazetteer, not access to the maps).
However, I also can't find it in Jacobstow in An Index to the Historical Place Names of Cornwall: Vol 1 - A to K which you can find at Google books, and that does cover farm names; there is a Berry Court or Burycourt or Barry Court farm, which is a bit of a stretch.
One way of locating it would be to look at census records for the parish (and the order of entries) plus the enumerator's description of the boundaries of the area they covered. With that information, it may be possible to locate the property between two other properties by following roads/tracks between them on a map.
The 1837 tithe maps might also be useful. They're online at TheGenealogist but you need a subscription.
Keep an open mind about the possible spellings: Barah, Bara, Barra, Bearah, possibly even Bear.
I can't locate Barah as an address in Jacobstow in the 1841 census which suggests either that the farm was subsumed into another farm (in which case you might find a property transaction in the local Archives) or that Barah wasn't actually in Jacobstow. Were there other events for the same family in Jacobstow? Or might they have been visiting (Possibly her mother) at the time of the baptism.
Your best bet may be to contact the OPC for Jacobstow by email via their website and ask if they can help.