POOR nutrition...

So I'm having a problem that I need some advice on. I'm a very healthy person, I eat little to no processed foods, or sugar. I eat mostly veggies and fruits, with some meat eggs diary. (Almost everything homemade). I also do Blw with my 8 month old and she eats everything I eat. Nutrition/health is very important to me and I want her to have that same awareness to food. The problem is my sister and my niece just moved to my state and my niece has a very bad diet. Her mother eats healthy as well, but she gives her pizza, frozen fries, nuggets, yellow rice, bread, and packaged mac and cheese. I just get so upset when I see her eating these things or I have to make it for her. I feel bad for being upset but I can't shake the feeling,, i know BLW also teaches not to force feed but she just also gives her all these bad things instead of offering healthy foods.( She's 7 btw.) I worry about her, all she eats is junk. I know she's not my kid but I hate to see her eat that way. Am I wrong for getting upset? Would you? Would you help make her the junk food?, or say I don't want to help aid her bad diet. I love my niece but her really bad diet/ poor nutrition really irritates me.