How do I tell my friend with anxiety to shut up?

Ok so I have this friend who NEVER SHUTS UP. She s a complete narcissist. Every time I talk to her all she does is talk about herself and the things she wants to talk about, whether it s just her and I or we re with a group. No one can ever talk about things they want to talk about because then she ll change the subject back to what she wants to talk about. I sit with her at lunch with like 5 other people and I know next to nothing about these people that I sit with virtually everyday for 30 minutes for months. I don t think she does it on purpose and it s not very noticeable so to say. She has a big personality and is funny, loud, and passionate, but I want to find a way to tell her that she needs to shut up sometime and not cut people off all of the time. I need to do this in the most gentle and constructive way because she also has very bad anxiety and sometimes will have to miss school because of how intense some of her panic attacks are.