Actually Robinson was a very common surname in Ireland in the mid-19th century particularly in Ulster province but also found in many counties of the current Republic of Ireland.
I searched on the subscription site Roots Ireland and like you did not find Jane with father George in Oldcastle or any parish in Ireland.
I then searched on another subscription site Find My Past and they had a April 8 1831 baptismal record for a Maria Joanna Robinson with father George and mother Maria Nordon. The church was the RC Church of St. Nicholas in Dublin city on Francis St.
Jane could be a variant for Joanna. I would treat this record as a lead. Possibly she was born in Dublin and later moved to the Oldcastle area.