Perhaps from yiddish Shayne/Shayndle/Shaydle etc (meaning "beautiful", german scho"n,)
http://data.jewishgen.org/wconnect/wc.dll?jg~jgsearch~model~GNDB_POLA~SIDEL~GD~!1!!2!!3!~0~USRECORD1165
Going from "beautiful" to "princess" is not such a big leap...