pass away unmarried

a) Nothing wrong with the grammar, but spinster is very archaic. Ok if you're talking about eg Jane Austen, but it's rarely used now because of its negative connotations.

b) I initially thought She passed away unmarried sounded odd and that it was a matter of collocation - that he only expressions that usually follow "pass away" are time references He passed away three years ago or adverbs related to the manner of death She passed away quietly / in her sleep. But Google it and you'll see lots of examples which, in context, sound fine. As always - you can't evaluate language use out of context in the sort of individual sentences you provide. Always give the surrounding text.

Good answer. Thank you.