Excessive tanning and getting sunburns causes skin cancer. I have a friend who had melanoma that spread to her ovaries, and now she needs to get screened constantly and get every large mole removed just to make sure it doesn't come back.
At the very least, yes, it will make her look old in short order.
Eating Skittles and chicken nuggets MAY lead to weight gain that MAY lead to obesity that MAY lead to heart disease and cancer and all that. So IMO what she's doing is more unhealthy.
I wish I could hug you through the screen right now, Hawingbird.

I hope you're doing better now.
I'm naturally ridiculously thin. It's not healthy for 90% of women out there. No one should
aspire to this. And it will harm me in the long run, because my grandmother had osteoporosis (died being bedridden for a year after breaking her hip) and my mom was diagnosed with it at 52. At 29, I'm fighting to build up muscle and bone, and doing it fast, because starting at 30 I will start to lose it more than build it up.
I just want to tell every woman out there who's going through an eating disorder, that being skinny doesn't solve anything. It's just the shape of your body, it doesn't make you look at the world differently.