That would depend on a couple of circumstances. Normally
FMLA covers "spouse", "parent", "son", "daughter" but not a grandparent. However if the grandparent is in loco parentis - took the place of the child's parents for day to day physical and financial support - then the
FMLA regulations will apply to care giving for the grandmother the same as if the grandparent were her parent. (29 C.F.R. 825.122 defines spouse, parent, son, daughter)