I was born in Poland and have several Genevieves in my family. The Polish form is
Genowefa. Genyusha would be a nickname but the spelling does not follow Polish orthography. The form she is using is most likely Yiddish. In Polish this nickname would be written Gieniusia and
Genya would be written Gienia. I don't know how her family would have pronounced it in Yiddish but in Polish it's gyeh-NYU-shah. I would not be given as a full name these days as nicknames as full names are not permitted. Also in Polish it sounds cutesy and childish.