According to the catalogue at the record office she was Sarah Goodyer of Bury born 1791. Most of the diary entries are dated between 1803 and 1806, recording visits made by her (unnamed) uncle and her aunt, usually separately. I suspect the uncle is travelling on business and the aunt (usually in the company of other ladies) might be visiting family or friends. She does not mention her parents or any siblings or a school. There are also entries saying that Mr ... or Mr and Mrs .... came to dine, so they were entertaining friends or business associates. There also odd entries about births and deaths, the earliest being 1774. Either the diary was started by someone else or Sarah was told about the event as it predates her supposed birth.
There are also records of books borrowed or lent to people - these are very faint, possibly written in pencil. Many of the later entries are just of grocery items purchased and the prices.
The London reference looks like it holds together. I think the two references to places (on the same page) are in a different hand and the phraseology is more adult.
The only Sarah who fits the birth year was the daughter of Clement Goodyer and Sarah (nee Young). Sarah Young died in 1795 and Clement remarried (another Sarah). I know of two children born to them William bapt 1798 and Ann bapt 1800. I believe daughter Ann was the one who gave birth to an illeg daughter in 1816. The bastardy bond says the child was born at the house of Clement Goodyer putative father Richard Hills.
If Sarah's father and half sister were still alive when she was writing the diary, I am surprised there is no mention of them.
There is a marriage of a Sarah Goodyer in Bury in 1812 to a Richard Humphries. The diary Sarah would be 21, so a possibility that it is her.
The diary was written in blank pages of Rider's British Merlin for the Year of our Lord God 1756...... with Notes of Husbandry, Fairs, Marts, High Roads, and Tables for many necessary Uses. Compiled By Cardanus Rider.
I guess this is the sort of book which would be published annually, so might be around the house long before Sarah started writing in it, so some entries could be by someone older.
The diary was deposited at the Record office by Mrs. M.A. Killip, of Barnham, Sussex, 12 March 1979.