"Penny" was the nurse to Ben Grimm's uncle, Jacob Grimm, who was recuperating from an accident which took the life of his wife. Despite their age difference, Petunia married the much older Jacob Grimm and together they helped raised the orphaned Ben Grimm. 
Ben Grimm had made numerous references to Aunt Petunia over the years, describing her as his favorite aunt. Eventually, Petunia visited New York City to ask the Fantastic Four to help with a mystery in her hometown of Benson, Arizona. This was the first time other members of the Fantastic Four had met Ben's oft mentioned aunt.
She was brutally murdered by the Marquis of Death in order to torture Ben Grimm, as part of an attempt to destroy the Fantastic Four.