If it's a "nutrition" shake, and it's got the necessary vitamins and minerals in it, then she's probably ok (even if it seems weird). However if she's not getting the nutrients that she needs, you may need to see if she'd be willing to talk to doctor or therapist.
She might have a texture issue. I know people who can't stand the textures of certain foods, maybe hers is more broad of an issue. Is her weight an issue? If so, she needs an intervention, some tough love, for the sake of her health. Good luck. I know it's not easy. I had an anorexic friend in high school, & the fun part was a friend of hers I couldn't stand who would tell her how great she looked! Her boyfriend, parents, & I had to team up to keep that girl away from her, & get her into an inpatient program to take care of her.