I have an acquaintance who is a very cold, logical sort of person. She likes to make the 'best decision' for any situation, and wouldn't hesitate in a "kill one to save ten" sort of scenario. She doesn't celebrate any holidays (including her birthday) as she sees no good reason to. I could easily see her as a comic book villain, but at the same time, she's one of the most caring people I know. The past week she would gladly wish people a "Merry Christmas" or "Happy Hanukkah." If she hears you're sick, she'll make you homemade soup.
Perhaps the best way to describe her would be as a caring machine. If you were sick, she'd care for you better than anyone else, but wouldn't hesitate to euthanize you if the situation called for it, nor would she shed a tear.
I've been struggling to come up with a word for her, and simply calling her logical or "a machine with a heart" seems inappropriate. Is there a word for a person that is both very caring, but will not hesitate to be cold and logical when necessary? I know this is the English language stackexchange, but I'd settle for a word in another language if there's no English equivalent.