The first time she lost a grandchild, he was nine. She'd tried to minimize the damage--gave Subaru gloves, and lectured Hokuto on the Sakurazukamori. (Subaru was too naive, but Hokuto would watch out for him.)
The second and third time she lost a grandchild was seven years later. She'd recovered his body from the Sakurazukamori's illusion, but could not rescue his mind. Hokuto sacrificed herself for her brother's mind, ignoring the cost on his soul.
The final time she lost a grandchild was with a hand through a heart. It would have broken her less if Subaru had died.