How well I knew Her not — Pain Puff

This poem talks about some dishes called pain, like pain puff, and a woman next door to Dickinson.

How well I knew Her not 1
Whom not to know has been
A Bounty in prospective, now
Next Door to mine the Pain.
(F.813/J.837)
[1] knew Her not:: a neighbor whom Dickinson knew not about her cooking skill.
[2, 3] Whom, Bounty, now:: this woman (Dickinson knew not) has now become an expected bounty (boon, gift) due to the smell of pain puff.
[4] Pain:: Cookery. Applied, usually with qualifying word, to various fancy dishes, mostly containing bread; as . . .  pain puff, a kind of puff or small pie with soft crust (OED n.2 2).

Third course: Pears in syrop; great birds with little ones together; fritters, pain puff, with a cold bake-meat.——English Merchants (1866)

Bread is to be baked every day, pain-mains (small loaves or rolls) every second day——Domestic Memoirs of the Royal Family and of the Court of England (1860)

This poem was written in 1864. In 1856, Emily's brother Austin Dickinson married Susan Gilbert and lived in the Evergreens, next door to Emily. The poem can have a second reading against Susan. Bounty is the reward of taken a wanted criminal. Emily treated Susan as a criminal, and pain was Emily's reward to overcome Susan.

I knew not well enough of her (Susan),
whom has become someone I don't know.
The reward in prospective to overcome her,
now next door to mine, is pain.