Your sister may be suffering from social media addition - addicted to WhatsApp , Facebook etc. This is a psychological condition listed a under DSM . So Yes she does require counseling. There is no age for counseling. Even children come to us for counseling.
But do not worry. Counseling is a very simple process and your sister can come out of this with a few sessions of counseling
Next Steps
fix an appointment with a counselor. discuss this with your parents first.
Health Tips
what are your sisters favourite hobbies? for eg, if she likes dance, you can encourage or even force her to enroll into a dance class. or you can try gifting her a activity set - like quilling set/ knitting set/ art set. these are easily available and will very interesting too. encourage her to make something handmade for your family members using these. spending time on such will reduce her time spent on the phone