I used to be incredibly underweight at the same age as my SIL is now (16 and at sixth form). She has always been slim but still healthy looking. Over the past year she has started to look gaunt and her bones jutting out. She skips dinner in the evening and claims to her parents that she has tummy ache. She'll also eat a piece of cake (or something sugary) to make it look like she doesn't have eating problems, but she'll skip meals later in the day or only eat a few mouthfuls.
I tried to raise my concerns with my MIL but MIL says that her daughter is 'lovely and slim' and she's lost weight due to a growth spurt (she hasn't grown in years and is the same height as me so I'd notice). I love my SIL and I've known her since she was at primary school. She loves spending time with me and my daughter (her niece) probably because me and her brother are in our 20s and young.
It's starting to really trigger me now that she keeps losing weight. I thought I'd recovered, but I actually dread her coming round to visit now. I'm not sure what I am asking, but I just needed to offload. Thanks for reading.