I certainly would stop short of shutting the door in her face but a simple, "I can't talk right now" might suffice. If that doesn't give her the message. More direct then measures should be taken. Still, I think the gentle approach would serve you better. Come right out and use the boundary word. Tell her the two of you need to sit down and discuss your boundaries. Be honest and let her know you are having difficulties with her ignoring them. Is there something you would in fact feel comfortable with her helping you with? Could you make a concession on this point?