What is the MOST likely reason that Ántonia wipes Jim’s face with a handkerchief?

Antonia was likely wiping his face because he was flushed and sweating. Jimmy might have been crying as well.

I saw his coils tighten—now he would spring, spring his length, I remembered. I ran up and drove at his head with my spade, struck him fairly across the neck, and in a minute he was all about my feet in wavy loops. I struck now from hate. Antonia, barefooted as she was, ran up behind me. Even after I had pounded his ugly head flat, his body kept on coiling and winding, doubling and falling back on itself. I walked away and turned my back. I felt seasick.

Antonia came after me, crying, ‘O Jimmy, he not bite you? You sure? Why you not run when I say?’

‘What did you jabber Bohunk for? You might have told me there was a snake behind me!’ I said petulantly.

‘I know I am just awful, Jim, I was so scared.’ She took my handkerchief from my pocket and tried to wipe my face with it, but I snatched it away from her. I suppose I looked as sick as I felt.