You are an extremely insensitive person who has clearly let your jealousy take over any sort of mature reaction.
I'm sorry you have only been trying to get pregnant for 6 months, that must be hard
It has taken me 9 months myself and a friend of mine 2 years and counting. Yes for some, such as your DSD it just happens.
People who struggle to get pregnant do get jealous of those who just fall pregnant easily. But people who struggle are those who are borderline infertile, have to go through grueling fertility treatments and have been trying for years and years. They are very much aware of how they should treat pregnant women regardless of what they are going through.
YOU have been trying for half a year and seem to think you can jump on the bandwaggon of those who are genuinely struggling. You really need to look at the bigger picture and maybe even read up on other peoples experiences. Some of these people will NEVER have children either and you have had one and will likely fall pregnant again when you stop desperately striving for a baby, stressing yourself out and reflecting your negative feelings on others.
You have no right to have taken it out on your DSD, who wants to be pregnant (no matter the circumstances of conception) and was probably quite hurt by your reaction. No wonder she was angry.
If i really thought you were struggling with conception i would advise you to seek help and support. But its clear you really are just a bit bitter about it all. Maybe you should apologise to her (doesn't matter who was wrong or right, be the mature adult in this) and should talk to and support your DSD, SHARE in her joy at becoming a mum (again REGARDLES of the circumstances of conception) and who knows, maybe when you do conceive you can support each other. Please try and salvage your relationship with her. She will need both you and your OH support as Grandparents.
I hope now that you have calmed down and thought about it you can do what is best for everyone. You are right when you say she IS too young for such a big thing, she is just a girl and it will be hard for her with no partner - all the more reason for her need for your support and advise. Don't "have a go" because she is pregnant and still smokes etc, just point her in the right direction with where to get the help for smoking and midwife support.
I hope this second post hasnt been too harsh and has actually been of some use to you. There is so much joy to be had in this situation and you don't want it to cause a family feud now, do you? Because you will ultimately be branded the bad person if you continue the way you are going. I hope everything works out well for you and your family :)