Don't lie! You would just heap guilt upon the way that you feel already. You would have this underlying feeling of doing something wrong the entire time you were on the Island.

From reading your other posts, it seems like your sister is an understanding kind of person. I think that you should explain to her that you feel very conflicted about going because of the situation with your niece. Just talk about every aspect of it with her. Let her know that you love her and that you would change things if you could. Life goes on even in the midst of unfortunate situations.

I second what Mr. Silver said.

That is my $ .02 worth.