The Lady's Yes
Tabors
Small drums used for dancing—this is a ball or party scene, not an intimate proposal. The music and crowd matter.
Fickle troth
"Troth" is a pledge or engagement. She's saying proposals made lightly get broken lightly—the casual setting undermines the vow.
Scorn recoils
If he scorns her for changing her mind, it rebounds on him—he's the one who proposed at a dance party instead of seriously.
As the thing is high
Marriage is "high"—sacred, elevated, serious. She's contrasting this with the low setting of the party.
Festive boards
Dining tables at the party. "Lead her from" means take her away from the social scene to somewhere serious.
Wives of yore
Idealized past wives, supposedly constant and faithful. She's promising permanence—but only if he earns it properly.
SHALL be Yes
The capitalization emphasizes permanence. A properly won "Yes" becomes irrevocable—unlike this flippant party proposal.