Question:
If an older woman who was never married before, gets married, does she need to separate after the first night if no blood was visible?
Answer:
She does have to separate. The reason for this is because chazal said “lo plug”- that all women, even if she is a young child that never did yet see, that she still has to separate. An older woman who has already seen is also included in this.
Sources:
Yad Halevi Y:D 80, Ashrei Hoish 26-12, Pardes Simcha 193-4.