What is the ruling on intercourse if a woman saw a light pinkish-yellow spot of blood, and then menstrual blood flowed after a period, and she does not know whether the spot was the beginning of menstruation and appeared before intercourse or after it, and whether the full flow of blood was before intercourse or after it?

There is no sin upon you both for what happened, as you did not intentionally engage in intercourse during menstruation. Sin is incurred by whoever commits a forbidden act knowingly and intentionally. If you are uncertain about the exact time of spotting blood, it is determined to have occurred at the latest possible time it could have appeared.