Grete Šadeiko (after marriage Grete Griffin; born 29 May 1993 in Türi) is an Estonian heptathlete.
At the 2010 World Junior Championships in Moncton, Canada she placed fourth with her personal record 5705 points, just one point behind Helga Margrét Thorsteinsdóttir.
In the fall of 2012, she joined Florida State University.