Can "She Stoops to Conquer" by regarded as a comedy of manners?

A comedy of manners is a dramatic genre that satirizes the customs and behavior of a specific group in society, usually the members of the upper-classes. She Stoops to Conquer would definitely fall into that category.
Right throughout the play, the ostensibly well-bred characters do everything they can to maintain social respectability while behaving in ways that are anything but respectable. It is this enormous gap between what the various characters think they are and what they really are that provides much of the play's humor.
Marlow, for example, likes to think of himself as a decent, respectable member of the social elite. And on the face of it, that's precisely what he is. Yet in the company of Kate, whom he wrongly thinks is a humble serving-wench, he behaves in a bawdy manner that would be thought unbecoming in polite society. There's also the little matter here of a well-bred young lady like Kate stooping to conquer in her lower-class disguise.
Goldsmith appears to be suggesting that this is far from unusual behavior in the upper echelons of 18th century English society. The manners and customs of this society are such that people are forced to wear masks to conceal their true identity. Far from conducing to propriety, such dissimulation leads to all manner of disagreeable behavior, which makes everyone involved look throughly hypocritical.