Hi, I have the marriages for All Saints Gt Marlow, there are no marriages for an Elizabeth Pearce, only an Elizabeth Piercy who married a James Harding 3rd June 1819.
Looked up marriages at All Saints Gt Marlow for a John and Sarah Pearce, none for a John Pearce, there was one for a John Pearcy to a Sarah Clark by Banns 13.2.1774 and a John Piercy to a Sarah Plucknutt by Banns 21.1.1799.
Was hoping perhaps to find an Elizabeth under the names Pearcy, Piercy in baptisms Gt Marlow. Only Elizabeth was the one you had found baptised 10.5.1804.
I'm afraid these details will not be of much use, sorry, but tried.
Noticed you had the surname Harris in Bucks, all my Harris ancestors came from Gt Marlow.
Kind Regards.
Kaysy (Harris)