is she the granddaughter???????? or some how related to this women

I think that woman is possibly her aunt cause the woman hints she knows what it’s like to be a second born(unless I took that wrong??) and Avery mother could have been her sister

I think it's brother. Avery is daughter of the previous duke who was the red haired women's brother. Avery being alive means that she is the legitimate heir and not the women and her son.

More likely she's the sister of Avery's father. The aunt does talk about a brother who ran away from home. If he was the heir, legally that would make Avery the rightful owner to everything the countess has.