This question appears to ask for a personal response. Your question states "trace your response to Ms. Purdy." I can't tell you the way that you, yourself, feel, but I can clarify what happens in the poem so that you can make your own assessment.
"How I Discovered Poetry" begins...
with the lines:
It was like soul-kissing, the way the words
filled my mouth as Mrs. Purdy read from her desk.
All the other kids zoned an hour ahead to 3:15,
but Mrs. Purdy and I wandered lonely as clouds borne
by a breeze off Mount Parnassus. (lines 1-5)
The narrator here is enthralled with the words that are coming from Mrs. Purdy. While other kids are zoning out and paying very little attention to the class, the narrator feels that poetry is just like "soul-kissing". The narrator says that she and Mrs. Purdy wander together, "lonely as clouds borne / by a breeze off Mount Parnassus." The line "lonely as clouds borne" is likely a reference to William Wordsworth's poem "I Wandered Lonely As A Cloud," and Mount Parnassus is a mountain that the ancient Greeks associated with Apollo and the Muses. The narrator feels a deep connection with Mrs. Purdy because of the beautiful poetry that she is reading, and she believes that their two souls have understood each other through this shared appreciation of canonized poetry.
However, the next day, Mrs. Purdy chooses a poem for the narrator to read. The narrator is the only person in the room who is not white, and this poem has been chosen "especially for me" (line 7). Although the narrator protests and says that she can not read the poem to the class, Mrs. Purdy "smiled harder / said oh yes I could" (lines 9-10). The poem is full of "banjo playing / darkies, pickaninnies, disses and dats" (lines 11-12). After the narrator finishes, she and her class are silent and cannot look at one another. The reader is meant to understand that Mrs. Purdy chose a poem that included particular dialect
and stereotypes of black people and made her only black student read it aloud to the class. This reading made the narrator uncomfortable and alienated her from the rest of her classmates.