16 year old sister pregnant need advice

My 16 year old sister is pregnant. She said she and the guy she had sex with wanted to do it without protection because he could " pull out". He didn't pull out in time and now she is pregnant. I don't know how to feel about this at all. She seems proud of herself and when she was about to tell me she told me not to stress because I need to think about my unborn child. Oh yeah did I forget to mention she is only 3 weeks behind me.