How can I interpret "not so + somebody"
The construction not so followed by a noun phrase and treated as an independent clause is quite common in written and spoken English. You can see examples from the Corpus of Contemporary American English (click to expand usage examples).
In this case, so means:
3 Referring back to something previously mentioned.
3.1 That is the case.
‘“Is it going to rain?” “I think so.”’Source: Lexico — so
I think so in the above example means:
I think that is the case; I think it is going to rain.
Not so, as used in your quote, means that is not the case.
These poor fellows bear pain and mutilation with unshrinking heroism, and die or are cut up without a complaint. Not so the officers, but we have nothing to do with the officers.
That is not the case for the officers; the officers do not bear pain and mutilation with unshrinking heroism. (I think she means that the officers whine or fuss instead of remaining quiet.)
Here are some examples from the corpus:
Just the other night, while he and his son, Robert, were at a restaurant, the waitress asked Dave for proof of age before serving him a beer. Robert thought that was hilarious. Not so his dad.
(MAG Newsweek)That was not the case for his dad; his dad did not think it was hilarious.
As Michael Jackson got weirder, his creative output got more and more tame. Not so his biggest rival.
(BLOG The 50 Greatest American Weirdos)That was not the case with his biggest rival; Prince’s creative output did not get more and more tame as he got weirder.
When a comet is dim, astrophotographers can compensate with longer exposures and faster film. Not so our eyes.
(ACAD Mercury)That is not the case for our eyes; our eyes cannot compensate with longer exposures and faster film.
This well was gushing oil, not burning, James says, and it was simple to shut down. Not so the hundreds that were ignited.
(SPOK ABC Nightline)That was not the case with the ignited wells; the ignited wells were not simple to shut down.