I don't know what Germanic language features -wen as a name element. The protogermanic form of the quoted name element is *WUNJA and it occurs in names like Wunibald as a first element. In Anglo-Saxon, it becomes wynne (with an umlaut) and later it becomes virtually indistinguishable from WIN "friend".
The form -wen looks very Welsh to me where it derives from gwen "white" (feminine form). I'd read Ros(e)wen as "white
Rose" with a Welsh etymology.
This message was edited 9/11/2017, 8:23 AM