Clara, returning to Santa Fe under the care of her energetic and affectionate relative, found that the deluge of debt would cover town house and haciendas, leaving her barely a thousand dollars.

She was handsome and accomplished, but she was an orphan and poor.

The main chance with her seemed to lie in the likelihood that she would find a mother (or a father) in Aunt Maria.
Yes, there was another sustaining possibility, and of a more poetic nature.

There was a young American officer named Thurstane, a second lieutenant acting as quartermaster of the department, who had met her heretofore in New York, who had seemed delighted to welcome her to Santa Fe, and who now called on her nearly every day.

Might it not be that Lieutenant Thurstane would want to make her Mrs.Thurstane, and would have power granted him to induce her to consent to the arrangement?
Clara was sufficiently a woman, and sufficiently a Spanish woman especially, to believe in marriage.