"There is a woman with a snapper."

So far, I haven't found a clue to this use of the word "snapper" (1851) to describe an energetic, irrepressibly attractive woman at any of the 19th century slang websites so far.

Here is part of the paragraph in which the word appears, in a letter (dated August 8, 1850) from Evert Duyckinck to his wife Margaret Duyckinck, reproduced in Steven Olsen-Smith, Melville in His Own Time (2015):

We passed on among the 7000 Shaker acres by the immaculate yellow houses, glazed like a pail, the red barns and the bricky natives, by well cultivated fields to the Hancock village where we saw the huge barn & where Mrs Morewood driving a pair of horses with three ladies had come on to meet us—There's a woman with a snapper. She is to be the owner of this house next year & I must tell you more about her—

What is its origin and what would the man who used the word and the man who read the sentence visualize when using the word?

Solution 1:

Mitford Mathews, A Dictionary of Americanisms on Historical Principles (1951), offers this entry for the word snapper:

snapper, n. 1. = snapping turtle. [Citations from 1796 forward omitted.] ... 2. A cracker at the end of a whip. Usu. transf. in the sense of a word or phrase giving a smart or pointed finish to something. [First three cited examples:] 1835 Hoffman, Winter in West I. 179 Jim cracked his snapper. 1857 Holland Bay Path xiv, You'd a said twenty lashes ... and Mr. Moxon would 'a said twenty Amens on the end on 'em for a snapper. 1895 Mark Twain How to Tell a Story 226 (R.) A humorous story finishes with a nub, point, snapper, or whatever you like to call it.

In definition 2, the "cracker" refers (I believe) to a bit of thong attached to the end of the whip to give it (when used properly) an extra-loud cracking sound. I have seen and used bullwhips that have this extra piece of thong on them, but I haven't heard them called "crackers" (or "snappers").

The citation from 1835 uses snapper in its literal sense, and could very well be taken to refer to the entire whip; the two later citations use snapper figuratively.

The word appears in its literal sense in Philip Paxton, A Stray Yankee in Texas (1853), in the context of a hostile interaction between the Yankee (Green) and a mule (Brandy):

GREEN. There, take that (attempting an application of the whip, and only succeeding in getting a smart rap with the snapper upon his cheek). Rot these darn fool whips!—as long as the moral law'n the ten commandments with the hull book a Revelation for a snapper.

After various attempts, Green began, as he said, "to get the hang of the thing," and then commenced a race around the lot, the Yankee cracking away at the mule and getting rather the larger share of the lash himself, until he finally cornered his antagonist in a kind of cul-de-sac, formed by the junction of the fence and stable at a very acute angle.

Evidently, in the sentence "There's a woman with a snapper," the snapper is a whip, which makes sense given that the woman in question (Mrs. Morewood) is described as "driving a pair of horses."

Solution 2:

A "snapper" is an Irish slang word for baby. From Collins English Dictionary:

snapper (ˈsnæpə)
6. informal Irish a baby

The word is still in use today in Ireland, and also widely understood in Great Britain. See e.g. the 1990 Roddy Doyle novel The Snapper, about the pregnancy of a young unmarried woman, or its 1993 Stephen Frears film adaptation.

It seems obvious that "a woman with a snapper" would simply be a woman with a baby or small child, rather than a woman carrying a fish or whip.

The word "snapper" has been in use in Ireland and Britian for centuries, but because it has several meanings, I haven't been able to find a source for it being used specifically for a baby in the mid-nineteenth century. It would of course not be unusual for an Irish word to have entered American English at that time.