Yes, my dd13 is exactly that way. My dh was hesitant about encouraging our dd's interests when she was very young as well b/c he thought that they were unrealistic and/or dangerous. Mine will be 14 in a few months and is entering 10th grade in the fall.
I have old mommy and baby swim class cards on which the instructors noted that she was a "fish." She has been drawn to the water since she was a baby. At three, she wanted to be an underwater photographer of manatees. That later became a marine biologist with a specialty in manatees and other sirenians. That then became marine mammologist with, again, a specialty in sirenians. She's contemplating tide pool biology now b/c she really likes the pacific Northwest and feels like she might be happier there than Florida.
She's been a member of the Save the Manatee Club since age five, has contacted some of the schools she is interested in attending for undergrad school to discuss her high school class choices, and got open water SCUBA certified at age 12 (she's been diving with an indoor SCUBA Ranger program since she was 8, which was the youngest she could start).
I, obviously, cannot tell you if this has continued on to career yet b/c she's got a few more years of high school, but I'd be really surprised if her ultimate career choice isn't in this general field. I am also, probably obviously, going to say that I support your choice to let her pursue this passion b/c I've done the same.
With a child this driven and unusually directed, I think that it would be a disservice to try to sway her from her love.
eta: I just read part of your post to dd13 and told her that someone was posting about a kid like her with a long term passion. Dd says that it is "awesome" and that she hopes that she has a kid like that one day and that your dd is going to be this amazing surgeon who saves lives
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