How long does rape evidence remain present?

a girl I know was raped and it happen like three days ago...if she go to the doctor would there still be DNA inside of her? Yes...at hand is a good possibility. Get her to the hospital, police station, or doctor pronto. Tell her to bring he panties she be wearing that night. If they cannot attain DNA from inside her, there is a coincidence they can get it from the underwear she be wearing.
Women naturally 'ooze' after sex as a inborn way to lubricate the vagina to prepare for fertilization. That ooze and DNA probably seep onto her panties which would also help her.
Yes, if she did not douche. She also should speak to a rape crisis center as she could end up have Post Traumatic Stress Syndrome. Your are a great friend so see if she will get checked out. She desires to be checked for STDs also.