P.B.
Hi T.,
You show a great deal of caring in bringing up this issue.
If your step sister is talking with you about other things, perhaps she will discuss her feelings about her sexuality with you, if you are open and supportive and patient enough for the conversation to happen without trying to rush things. As a mother and adult, you can encourage her to ask questions and then guide her to speaking with one of her parents. Know that she may choose to speak with her birth mother first. With your support and encouragement, she can learn a lot about the importance of discussing the bigger events and issues in her life with trusted loved ones.
Good luck,
J. B
Parent Coach