I assume you mean Laura who married William Mullen.
I suggest getting Laura's death certificate. If she died in Pennsylvania the only way to get her death certificate is through the PA Dept of Health. If she died in Delaware County check with the Delaware County Historical Society for her obit. Does anyone in the family know where she is buried? If so check with the cemetery office. They should be able to at least give you a burial date and of course check to see if she has a tombstone. Knowing her exact date of death (at least within a few days) will make it much easier to get the death certificate and obit.
Since she was Quaker check with the Friends Historical Library at Swarthmore College and Friends Historical Association at Haverford College. They may have a number of Quaker records that could be useful.