What physical action in the novel cause sal to ask herself “was that why my Mother left”

From the text:

And that surprised me. I had already noticed how tense Phoebe's whole family seemed, how tidy, how respectable, and how thumpingly stiff. Was I becoming like that? Why were they like that? A couple of times I had seen Phoebe's mother try to touch Phoebe or Prudence or Mr. Winterbottom, but they all drew back from her. It was as if they had outgrown her.

Had I been drawing away from my own mother? Did she have empty spaces left over? Was that why she left?