Her ability, like so many of the useful tasks she had learned as a child, to sew a fine seam, though sadly diminished with the passage of time and her failing eyesight, remained a marketable skill.
Those are called "suspensive sentences," and in the 21st Century, they're no longer elegant. But I still see them a lot, usually, I'm sure, not the result of the search for elegance but due to a lack of reading aloud! If you'd read this sentence aloud:
The chances that the progress of their passion over the summer will lead to lasting love are slim.
...you'd probably hear that the meaning of the sentence gets lost by the separation of subject and verb. Many "too complicated sentences" are too complicated not because of length but because of this separation. I can distinguish the main clause by diagramming the sentence (but I can't do the cool diagonals in Blogger):
The chances| are/slim.
The progress, etc., explains the chances, but as there's yet another clause (subject/verb) in there, the modifier can lead to confusion.
Here's a simpler sentence, with all the same words:
The chances are slim that the progress of their passion over the summer will lead to lasting love.
That remarries the subject and verb while keeping the modifying clause. Now there's also a guideline that modifiers should be near the word they modify, which is probably why the original author put "that the progress..." (the relative clause) by "chances." Sometimes there are two or three imperatives for a sentence, and you have to prioritize (or rewrite the sentence entirely, which is often a better idea). Here, because "slim" is a subject adjective (it just modifies the subject-- you could say "The slim chances") and the verb is "are" (which is like an = sign), so in a way, the relative clause can be seen to modify the entire main clause, not just the subject. (In fact, writers often create clauses -- chances are slim-- out of adjective/subject just so they can make a complete sentence-- it's a way to avoid fragments.)
Point is, sentences can be recast, rearranged, rewritten. There's nothing sacred about the first sentences that embarks from our mind onto our page. Simplification, or at least sentence awareness, will let us add on to the basic sentence without adding confusion.
This is something I frequently find myself editing in my own and others' work. In fact, that "diagramming sentence" above started out as a suspensive sentence because I started it with "Diagramming the sentence.... much in between here... can distinguish the main clause." Then I rewrote it into a passive construction (arguably worse :): The main clause can be distinguished...." Groan. Third time's a charm. I know, it's still not a stellar sentence, but it's an understandable sentence.
Let's be candid here. What are the sentence problems you most find in your edits?