Mary exemplifies the self-sacrificing angel image of nurses that hearkens back to the origins of the profession itself - she puts her dedication to her work before romance and marriage. This story is unusual, however, in that it points out an important reality for female nurses, that they have to expect amorous reactions from male patients for whom they have cared, as a kind of hazard of the job. And although the self-sacrificing angel is a stereotype, where there's smoke there's fire as they say, and there is an element to nursing that demands a dedication to the job because it is a helping profession. Importantly, this is something that a potential mate for a nurse would do well to understand. A nurse married to a man who doesn't see this about nursing is likely to experience problems when her husband starts feeling that he's being sidelined by his wife's job.
So when Mary backs out of the chance to marry Ray, realizing that she needs a man who understands and accepts her commitment to nursing, it puts the book in a kind of advice-giving category. Even with the changes that have taken place in the nursing profession since the 60s, and there have been big changes, this much is still true about nursing for most. If you're a nurse, you need your partner's support because it is a demanding, although rewarding profession (see the responses Mary receives from various patients, that do somewhat reflect reality).
Mary's real interest is in Dr. Will Ames, which tends to support another media stereotype of nurses from the period, that women become nurses so that they can marry a doctor. However, even though Will is clearly interested in Mary, the two haven't figured out a way for their relationship to move forward in a mutually acceptable way that also harmonizes with their work commitments. In an old style heterosexual patriarchy, where the woman stays at home and the man goes out to work, this problem is of a different nature.
Pencil artwork is by John Romita, Sr.