Should I say anything?

Okay, last week there was not enough room to sit at lunch, so me and my group sat with the popular girls. anyways, one of them sat across from me. We had been given a sandwich and fries for lunch, she just picked at the sandwich, didnt eat it, and then broke up her fries into small bits, she ate a couple, but thats it. I've noticed that sometimes she doesnt even get lunch either, she just skips. She always keeps her hair up also, but one day she left it down, and it was all dead looking, it was weird, it looked like if someone ran a brush through it, it would fall off. Now, i know this is none of my business, but i used to hang out with them, and she used to be a pretty good friend of mine, and i still kinda care about her. I'm worried, i want to tell my frinds, to see if they had noticed anything, but i dont want this to turn into a big deal. So, what should i do? Should I say anything, or keep my mouth shut? Silent_Scream