Yes, Katherine Ann Porter uses indirect characterization (as opposed to direct characterization) to describe the heroine of Miranda. Before we begin to explore the "how" of Porter's method, let's explore the "what" in regards to the definition of indirect characterization. Put simply, indirect characterization is used when an author shows a character's personality only through their words, actions, and (sometimes) appearance. In the case of Porter's book, which has an autobiographical heroine, Miranda, indirect characterization would be mandatory in that the book is written in the first person! In Porter's novel, appearance of Miranda is actually less important, so it's important for us to focus on both words and actions. Now it's time to explore both.
Even though appearance is the least important here, let's explore it anyway. Here is one significant quotation in that regard:
Adam and Miranda, twenty-four years old each, alive and on earth at the same moment.
Here we learn that Miranda is 24, most likely beautiful, and "alive." As for appearance, we can imagine a young woman just approaching the prime of her life and, unfortunately, about to be ravaged by the horrors of the First World War.
Second, and more importantly, we can see Porter's indirect characterization in Miranda's words. One of the best quotations from the book that shows Miranda's personality is as follows:
Don't you love being alive?" asked Miranda. "Don't you love weather and the colors at different times of the day, and all the sounds and noises like children screaming in the next lot, and automobile horns and little bands playing in the street and the smell of food cooking?
Of course, she is talking to Adam here, but she shows herself to be focused on the externals of the world (as opposed to the internals). Miranda, at this point, shows herself not to be very deep, only focused on the surface level. Just look at what she focuses on: weather (very often the subject of pointless conversation), colors, sounds, children, car horns, bands, smells. These are all related to the senses and not to deep thought.
Now, look at how Miranda changes as she experiences the unconsciousness due to her fever of influenza. In that unconscious state, where suddenly, senses have no meaning, Miranda admits the following:
[I suddenly feel] quiet instead of the noise of the jungle, serenity instead of violence, purity instead of corruption, understanding instead of separation.
Therefore, for Miranda, her experience of the flu and the resulting unconsciousness expand her awareness. In regards to Meyers-Briggs personality type, she ceases to be an "S" focused on sensory experiences and begins to approach the "N" finally seeing more of the thoughtful intuition. It often takes a life changing event (such as serious sickness, hospitalization, and unconsciousness) to change a personality type.
Second, we can see Porter's indirect characterization of Miranda in her actions. Specifically, I want to talk about one action in particular: denial. Miranda continually denies (as does Adam) that her lover might be killed in the war. Ignoring this possibility (and burying it deep within the subconscious) allows Miranda to go on through the surface level, refusing to deal with the intense emotions of death.
“Shut your eyes,” said Miss Tanner.
“Oh no,” said Miranda, “for then I see worse things."
Thus is the best quotation showing Miranda's action of denial. By the end of the novel, Miranda is forced to deal with the mortality of Adam as well as her own mortality and becomes a bigger person as a result.
As you can see, Porter uses both Miranda's words and Miranda's actions to indirectly characterize this particular autobiographical heroine. Miranda is focused on externals until she experiences unconsciousness. In this ways she ceases to be a superficial person and explores the depths of her reality.