All perfect praise be to Allaah, the Lord of the worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
You did well when you chose a girl who is apparently adherent to religion. Appearances are indications of what is beyond them. It is said, “What is bred in the bones will come out in the flesh.” The Prophet, sallallaahu ‘alayhi wa sallam, said: "A woman is married for [either one of] four: her wealth, noble descent, beauty or religion. So, marry the religious one, lest you should lose." [Al-Bukhari and Muslim]
You also did well when you performed Istikhaarah (guidance-seeking prayer, according to the instructions of the purified Sunnah. Allaah The Almighty will not fail whoever seeks His guidance.
As long as you chose an apparently religious girl, performed Istikhaarah, and consulted wise people, then you are following the right way. However, you have to verify the truthfulness of the claims on the delinquency of this girl, and act according to your investigations. If it turns out that such claims are mere rumors and the girl is religious and well-mannered; then, you should seek the help of Allaah The Almighty and go ahead in proposing to her regardless of the rumors. If it is proved that she is indeed an immoral girl, and there are no indications of her repentance, we advise you not to engage her. The Prophet, sallallaahu ‘alayhi wa sallam, said: “Marry the religious one, lest you should lose.” However, if she has sincerely turned to Allaah The Almighty in repentance, it should be known that a person who repents of his sin is like a person who did not commit the sin. All humans commit sins repeatedly, however, the best among them are those who frequently repent.
Allaah Knows best.