We had defended ourselves since memory against everything and everybody, considered all speech a code to be broken by us, and all gestures subject to careful analysis; we had become headstrong, devious and arrogant.
intrude in other people's affairs or business; interfere unwantedly
According to the chosen definition, one usually meddles in another person's business; one does not meddle someone else. But Pecola's use of the verb that way emphasizes her passive victimization (as well as her shortened education); it is also heartbreaking because she could have benefitted from more meddling by concerned friends and adults. But the conversation is actually one Pecola is having with herself, because she has gone mad.
Why are you so busy meddling me?
I just wondered. You don’t talk to anybody. You don’t go to school. And nobody talks to you.
How do you know nobody talks to me?
slender stem-like structure by which some twining plants attach themselves to an object for support
The use of the word "tendril" emphasizes Pecola's tender (vulnerable and easily crushed) nature and youth. But while a tendril would attach itself to an object for support, Pecola is alone and jerking to the beat of her own drummer.
She spent her days, her tendril, sap-green days, walking up and down, up and down, her head jerking to the beat of a drummer so distant only she could hear.
"Sloven" is a noun but the narrator is using it as an adjective. While Claudia could be seen as coarse and obnoxious for ignoring a hurting Pecola, in the example sentence, she was wondering how she could have been so slovenly in her planting. She had believed that God would grant her wish to help Pecola's baby live, if she gave up the money from selling the seeds. But Pecola's baby died; thus, Claudia assumed that her planting had been done poorly.
Our flowers never grew. I was convinced that Frieda was right, that I had planted them too deeply. How could I have been so sloven? So we avoided Pecola Breedlove— forever.