How do you stop a rapist before they become a rapist? How can you know (or at least reasonably assume) who is or isn't going to rape someone?
And wtf is a whistle gonna do? Seriously. Most people are too scared to try to help. She might get lucky and be within earshot of a nearby "hero" archetype... maybe.
I still say that if a woman really wants to be "safe" (as possible), she'll put in the work to gain physical strength and martial knowledge sufficient to equal or exceed the brute force of any potential rapist, and not willingly put herself in compromising positions (such as being "legally incompetent after just one drink"), because she cares enough about protecting herself, to take it seriously. And if she happens to get attacked, overwhelmed, and successfully raped... then fuck it, shoot the guy! Everyone would understand, IMO. I would anyway. If a woman killed her rapist during or immediately after the incident, i'd vote justifiable homicide. If the rapist rolls the dice and loses, that's his own damn fault.
Women need to be tough enough to fend for themselves, if they want to be considered "equal." That's part of the responsibility of independence: "the price of freedom is eternal vigilance." People everywhere are waiting to take your freedom from you, one way or another. You have to care enough to prepare to maintain the level of readiness required to stop someone like that. I've seen some very tough women who would make any potential attacker regret his choice of target.