I'm 24, I lost my grandmother - i went and saw her every chance i got when in the big smoke (once every three weeks) and yes, it was gut wrenching. i took it my my stride i felt i owed her.
My sister who is 26, couldnt handle seeing her but would listen to how she was going down hill. i also very, very suddenly lost an uncle with in 5 weeks of my nan's passing but i listened to any one who needed an ear.

your neice needs to wake up and realise death happens, people get sick and life isnt going to be happy happy joyjoy. its about how to handle it and how you grow from it (for me me with my nan i got her name tatto'd on my back).
she's going to be a teacher and life will NOT BE all happy go lucky some people will not get along with her or her views or what ever - is she planning on telling them to shhhhhh she cant take it?

I get its not easy to see some one you care for go down hill, and its painful to hear but really, give her a cup of cement and tell her to harden up. thats really poor form on her part to expect you to ignore what needs to be talked about so she can be "happy"