grandmahood
Same as motherhood, but for grandmothers. The longer version is 'grandmotherhood', but no one has the time to say it. The male equivalent for this term is 'grandpahood' and again, the longer version would be "grandfatherhood".
"Do you see Mary? Look how happy she is while holding her newborn granddaughter!"
"Ah, yes! She's definitely enjoying her grandmahood!"
"Ah, yes! She's definitely enjoying her grandmahood!"