Boston Funeral Records

Elizabeth Ashton passed away going through Boston with her family late June of 1856.  She was with the group that became the Martin Handcart Company.  She was on the Ship Horizon when she died, but in the harbor.  She died the day the company disembarked and headed to start their train journey.  The family had to leave just a few hours after her passing.  I assume she was buried in a pauper's grave.  I would like confirmation of this.  Does anyone know how to search funeral records for Boston?  I would very much like to find documentation of her burial.