Help!! How do I tell my 15 yr old she's going to be a big sister???

Tiffany
After thinking I would never have another baby (7 years of trying with ex husband with no success, not even a miscarriage) as well as other short term relationships, I learned a few weeks ago that I'm pregnant!! I've talked to my daughter about what if I got pregnant, all she says is no and won't say anything more. How can I break this news gently? Any advice is greatly appreciated.