Is my sister anorexic?

Hellooo :) I'm thinking my sister might be anorexic. It kinda freaks me out since I'm 13 and that kind of stuff really scares me. She's 17 years old, 5 foot 3, and I think she weighs 105 pounds. I'm pretty sure that's her weight, or around that weight, but she doesn't tell ANYONE her weight. I think that's what I heard the doctor say when I went with her for a physical, though. She weighs herself about 3 times per day and constantly looks in the mirror at her body shape. She is actually in really good shape! I wouldn't say she's underweight. She has a pretty flat stomach, almost a six pack. Her legs aren't skinny, nor are they fat. They look kind of muscular since she's a dancer. She always tells me to stop her from eating cookies and stuff, but it never really works. Like sometimes she tries to diet, but it's hard for her. But today she was lying on the couch with her elbows on her knees so that her stomach was hunched over so obviously there was a little "roll" out and my mom *playfully* says, "Look at that pooch" and playfully pokes her belly and my sister flipped out. She threw her phone at my mom's neck and started crying. Then my mom started crying. My sister has a glass and plastic phone and chucked it really hard at my mom. They have a REALLY bad relationship. Anywho, she clearly has some of the signs of anorexia (weighing herself obsessively, thinking she's fat when she clearly isn't, trying to diet, flipping out at a playful comment, not letting anyone know her weight) but then again, she doesn't obsessively diet either. Like just today, my sister and I had a large Pinkberry frozen yogurt with a bunch of toppings. Hahahah. She does eat kind of a lot, but she really isn't fat at all. I can understand where she's coming from, like I think I'm fat a lot of the time too. But I really am. But I don't obsess over it and weigh myself 200 times a day, I just try to exercise. So, do you think she's anorexic or just going through the self-conscious teen faze like me? Thanks a bunch!