Thanks for the feedback: yes, Catalina is very trusting, and always wants to be at peace with others. It's endearing if somewhat concerning at times. But this story is very much one of discovery for her and she will learn more as the story progresses.
Per nursing: I think it's more that she's helped her parents for years and since she doesn't have any ambition of her own, becoming a nurse like her mother (or at least an aid) was a likely enough career path. She was probably an indifferent student, not bad, but also never a high achiever either, and so I don't think she'd ever strive to go much higher. I also think Catalina (like Catherine Morland) has a lot of joy in life which spills over into any accomplishment that comes her way.
Of course, she's now being exposed to far more experiences than might otherwise have happened, so we'll see what happens.