What happens next? An alleged harassment victim doesn’t want to come forward

Q. An employee confided in a regional VP that their boss had invited a co-worker to have a drink in his hotel room while they were attending a conference. When she declined, the boss became angry. Now, the boss has reported the co-worker for leaving work early without permission. The employee doesn’t want anything bad to happen to her friend, but she can’t let this go without telling someone. The co-worker refuses to come forward herself out of fear of retaliation. What should we do?