Two more examples of spinster meaning an adult woman who owns property in her own right.
Strafford County Deeds 40:222
Jane Wallace of Epsom, Spinster, widow of the late Samuel Wallis of Epsom, deceased for $150.00 sold to John Wallis of Pittsfield, yeoman, 100 acres in Gilmanton that my late husband left to me by his will. Dated 27 May 1802. Witnesses: Joseph C. Wallace and Comfort Wallace (her children).
Strafford County Deeds 120:415
Benjamin Wallis of Sandwich, husbandman for $95.00 to Maryan (sic) Wallace of Sandwich, wife of Thomas Wallace, spinster, 50 acres in Moultonborough, dated 1 January 1821.
So you can be a widow spinster or a married spinster.