I don't think the was ever a more mature version of the Narsha sculpt, but there are a few different heads in the Narsha size range. They are currently Narsha, Shabee, Coco and Zihu. There may be closed, or half closed eye versions as well. Not sure if any of them looks more mature, though. I think it depends a lot on styling and face up. Could it be one of them, that is on your doll? If you bought a doll on the second hand market and the head doesn't seem to match what the doll was sold as, it is possible that it's a hybrid with a head from a different company, of course. A picture your doll would help a lot with identification.
@mikki Your doll is so cute! And that sweater is gorgeous. My Zihu (Claudia-Colette) - autumn version C.C. and apples I - leaves by Arengil Tajedinápravá, on Flickr
@mikki I'm glad you like her! C.C. - masquerade by Arengil Tajedinápravá, on FlickrMasquerade by Arengil Tajedinápravá, on Flickr