Boyfriends little sister

So my boyfriends little sister just turned 14 and is going into high school next year. She has been raised by a single father and two older brothers. I am her only female figure. She has a boyfriend and I feel like she’s ready for the, sex and birth control talk. Her dad seems like the kind of guy who would throw a temper tantrum if she said she needs to be on birth control. How to I go about talking to her about it without over stepping my bounds? Could I get her birth control if her dad won’t?