Hello Steve,
The name is actually spelled "Severija" in Lithuanian language but I have chosen to use the Norwegian spelling without "ij" in her Norwegian passport. The origin is the same as "Severin", "Xavier" and "Javier". In 'Lietuviu vardu kilmes zodynas' (Lithuanian name dictionary) the name is described as from Latin "Severina" or "Severinas" and with the meaning "serious, earnest, strict, severe, stern". (Her second first name is "Grethe" (meaning "pearl").
Regards, Jan