Eating disorder?

Hi I’ve been kinda worried about my best friend. She’s always been small and really skinny. But lately she hardly ever eats anything and when she does eat, she gets full really easily. If she eats dinner, it’s a very small dinner. I think she eats about once a day and if she eats they are small meals. I’ve noticed that she lost a lot of weight lately. In the past 2 weeks, she lost 10 pounds!! I’m not sure if she’s just naturally like that or if this is an eating disorder. I want to help her but I’m not sure how