Does a woman who stained like a niddah, still have to count 7 clean days if she is no longer menstruating or has had a hysterectomy?
Even an elderly woman, who sees a stain, must go through the regular niddah procedure of purity.
However, a woman who has undergone a hysterectomy (and does not have any part of her uterus) does not need to go through the niddah procedure, and she remains perpetually pure. This is the ruling of most authoties, though there are those who dispute this.
See Shut Zekan Aharon 2:50; Maharash Engel 7:12; Hilel Omer 85-6; Har Tzvi Yoreh De’ah 147; Chelkas Yaakov 3:14; Shevet Halevi 2:90; for a more stringent opinion, see Minchas Yitzchak 1:125.
For an elderly woman, see Shut Binyan Tzion (chadashos 11); Chelkas Yaakov 2:18.