Hi Stezza - this is Jane Austen's British English from Pride & Prejudice, dating about 1800-1813, and it is perfectly grammatical for its time. If you haven't read literature from this period it will give you a headache to start now. Your rewording is very clear & much better than Ms.Austens's for a modern audience.
This is the less pretty but more detailed (confusing pronouns) version.
At that instant, Elizasbeth felt that years of happiness (years of happiness in the future) could not make amends to Jane or herself (Elizabeth) for the moments of such painful confusion (as they were experiencing at this moment).
Hey, lighten up - I meant no offense.
Plenty of people have not read Austen or wouldn't recognize one sentence without context. And you did ask "Whose sentence is this?"
Perhaps knowing that shiness has been reading Austen for quite a while & has been submitting posts on P&P gave me a little advantage. Context is everything. I understood the quote as written but that's just me. This sentence is probably not the only instance in which "amends" appears alone in literature from this period.
As I said, your rewording is modern, accurate, & concise.
I was merely attempting to clarify the meaning of the original sentence, especially the pronouns.