The tune, an 18th C British drinking song called the "Hymn
to Anacreon", or "To Anacreon in Heaven", requires a singing range exceeding an octave and a half. Most of us could manage that in our youth, but by now at our age it has declined to under an octave. If you listen to the first 3 notes, she descended to an uncharacteristically low but necessary note on the word "say" and then had to work her way back up to "the land of the free" which is usually where people lose voice quality and tonality and above all accuracy. Professional singers of the operatic sort can do an octave jump above "free". The rest of us are just left panting. It also requires very precise use of breath, since both low notes and high notes require considerably more breath volume to produce notes of the same loudness than those notes in a person's "sweet spot".
As you are aware, singing was a recreational entertainment in the days before recording, and there were singing clubs everywhere for whom well known composers would compose songs so that amateurs could sing them. Pills to Purge Melancholy published by the Catch Club, a group of amateurs in London in the late 17th Century has songs composed by Henry Purcell. The songs were uniformly about sex and/or drinking, some of them quite explicit, as was the repertoire of the Anacreontic Society.
"The Anacreonticks were basically a bunch of young rakehells, endowed with far more money than was good for them, who liked to sit around and engage in such cultural pursuits as provided good excuses for getting filthy drunk, hence the emphasis on the more boisterous of the Greek gods."
For a more scholarly discussion see http://www.colonialmusic.org/Resource/Anacreon.htm
"William Lichtenwanger, "The Music of 'The Star-Spangled Banner,' From Ludgate Hill to Capitol Hill" The Quarterly Journal of the Library of Congress 34/3 (July 1977), 136-170. The song images are from The Nightingale, A Collection of the Most Popular, Ancient, & Modern Songs, Set to Music (Portsmouth, NH: William and Daniel Treadwell, 1804), pp.188-191, courtesy of Arthur F. Schrader
Ludgate Hill is the hill upon which St. Paul's cathedral in London, Eng. is built, and the road named Ludgate Hill was the home of many better class drinking places in the 1600s and 1700s.