Am I worrying about her for no reason?

I've been worried about my older sister. She's 22 and she's really skinny and she's always been that way, but because of college and moving a lot for internships she hasn't seen the doctor in over two years, if not more. Same with the dentist. She's 5 ft 3 and a 00 bearly weighs 100 pounds. I mean honestly, she looks healthy to me but I'm no doctor, and besides looks can be deceiving. Or she could have a issue on the inside.. Something that we can't  see. She just needs a checkup. So that's why I'm worried about her. Am I over reacting?