Catalysis of the transfer of a methyl group from S-adenosyl-L-methionine to the oxygen atom of a nucleoside residue in a small RNA molecule. Reaction: S-adenosyl-L-methionine + small RNA = S-adenosyl-L-homocysteine + small RNA containing a 3'-terminal 2'-O-methylnucleotide.
small RNA 2\'-O-methyltransferase