If she asks again, just say/keep saying, "What other days/time are you available to meet? That time is not convenient for me." Keep putting it back on her; you don't have the time, she has to pick a different time or you cannot participate. If she keeps pushing, say exactly that, "You have to pick another time or I cannot participate". If she keeps pushing still! Start saying it in a very annoyed tone of voice and/or tell her "It doesn't sound like I can participate in this meeting, call me for the next, please" and turn and walk away.