I would for sure talk about it little by little, as the need/occasion arises. I would for sure explain that it is an option that the world throws out and people sometimes choose but that it comes with heavy consequences - I have a couple friends who have been scarred for life with having had an abortion. It is terminating a human life, whatever terminology you choose. This baby doesn't get to live. And the woman/girl has to live with that the rest of her life. It can also have a negative health impact on the woman's body (even death for some). It is an option, as is adoption, keeping the child, all of those are hard choices to consider - the easiest one is to NOT put yourself in that situation, to wait until you're truly ready.
Your child needs to know your values, especially now that they've been seasoned with your life experiences & maternal wisdom, and that needs to be passed on to the younger generation. You are right in that the world today tries to devalue life and family and morality, and this is indeed dangerous. Dangerous to individuals and society both.
The reason I say to talk about it little by little is so that you dont give them more than they need/are able to understand. An analogy - my mom said I found some pads when I was a wee child. I asked her what they were and do you think my mom launched into an explanation of how women bleed each month etc? She just simply said it's like a big bandaid. And I was satisfied. (I'm sure my mom breathed a sigh of relief that I didn't ask for more, I know I would've!)
I love the rocket ship analogy. We have the choice as to whether to go on the rocket trip, get in the rocket, buckle down, and count down. Once it;s blasted off, changing your mind is a little late, the choice has already been made. It becomes a matter of life & death. It is not birth control. It is not a simple option to be easily decided on. It is a huge and heavy decision to make.
You dont say why this question was raised, if you are just preparing (kudos to you for this!) or if your daughter has been hearing/asking about it. 12 year old is not too young to bring it up, keeping it general and only getting to the level she needs/is ready for. I can see my 8 year old son asking what an abortion means and of course I would explain it to him in a little more general way than to a 12 yr old daughter or a 17 yr old son, etc. Ask her what she knows, what she thinks, and share your thoughts and feelings as you fill in what she doesnt know/understand or is incorrect on.