Perhaps you should consider why you want to talk to her and possible ramifications if it doesn’t go well? Not that I think you shouldn’t tell her. Then, though, set up a 1:1 with her, telling her that you want to have a private talk about something important to you. Yes, that will pique her curiosity but more importantly her mindset will be more prepared to understand that whatever you tell her is sensitive and hopefully she’ll be receptive and reserve judgment while you’re spelling it out.