I will have BCBS starting Jan 1st 2018. I have Medical and Durablw power of attorney over my 50 ur old sister. I’m her caregiver. Can I add her to my employee health insurance plan?

Adding an adult sibling to my employee health insurance plan starting Jan 1, 2018.  I have Medical and durable power of attorney of my older sister. She is 50 and is disabled. She lives with me, is a dependent on my tax return and I’m her caregiver. In all legal aspects, She is my dependent. Can I add her a a dependent to my new employee health plan?  My employee is switching to BCBS of Texas starting 1/1/2018.  It is open enrollment right now so I need an answer ASAP!!