If it's the wrong spot, I'm sure a moderator will move it.
They way I understand it, a woman will normally refer to her own adult daughter usually by name, usually with no honorific, although depending on the individual there could always be a '-chan' especially if using a nickname.
If the granddaughter in your scenario very young then calling that young girl's mother by name might be weird and confusing, in which case some version of 'mother' could be used. Almost certainly not an explicit 'your mother', because who's mother it is should be understood. If who's mother it is does need to be stated explicitly for some reason, then it would be "(granddaughter's name)'s mother"