How do i make the custodial grandparent let me see my 29 month old granddaughter?

my granddaughter was given custody to the fraternal Grandparent she has cut us off from her how can i make her let us see her we are her maternal grandparents we raised her from birth! we believe this ripping appart is a detrament to are little one! she is and we are devistated over this seperation!