I looked at the Bradford Co., PA info on Google and then looked at US Census for that county in 1810 and 1820. No sign of any Jennison. Maybe they owned property there but lived in NY? I've seen Sylvanus Jennison's name in a lot of records so it's helpful to know that he could be Dolly's son.
On FamilySearch.org I've been making a list of file numbers, CD's and PINs for Purley, Peter and Mehitible. There is a Mormon temple nearby where I could order the CDs or I might make a trip to SLC in the next couple of months.