Where does “-ы́ня” come from?

-ы́ня (Russian) comes from Proto-Slavic -yni, from Proto-Slavic -ni — one.

Ancestry of “-ы́ня”, step by step

Step	Language	Word	Meaning
1	Proto-Slavic	-yni	Denominal, forming feminine noun forms....
2	Proto-Slavic	-ni	one

-ы́ня — Etymology, Origin & Word History | Etymology Explorer