Hi, I (49) finished my first camino (Portugues) this September together with my son(20).
I was 18 too, when I first heard about the camino in school and ever since then I knew, I would go for it one day. Time went quickly and when I was in my thirties, my son about eleven years old, we listened a lot to the really funny audiobook of a famous German guy, who did it. I told my son that I intend to walk the camino one day, when he and his sisters are older. And he said: let's go together after I finished school!
I didn't take this for serious first, but he kept talking about it over the years and finally we did it one year after his German Abitur and hiked from Porto to Santiago. It was one of the best experiences in my life and I feel gifted and thankful for having such an intense (and unexpectedly funny) time. I can highly recommend this way, camino Portugues , which is said to be less exhausting compared to others. This might be an issue planning it with a 12 year old girl... We chose the coastal way on our first day, which is beautiful!
In total I suggest asking your daughter if she is really exited about doing the camino. If your companion is a teenager who hates hikes, walking and is in puberty on top: good luck! Your dreams might not be hers. Best wishes to you and Bon camino!