Quote 1
Like many people with a bold fondness for volunteering personal information, anything that suggested a direct question, a pinning-down, put her on guard (3.23).
Holly's unwillingness to answer direct questions reflects her active move to isolate herself from other people. This way she's always in control.
Quote 2
Her cheek came to rest against my shoulder, a warm damp weight. "Why are you crying?" She sprang back, sat up. "Oh, for God's sake," she said, starting for the window and the fire escape, "I hate snoops" (3.58).
There's a brief moment when Holly lets down her guard and invites someone in, but as soon as the narrator presses her she goes back to isolating herself.
Quote 3
"We sort of just took up by the river one day, we don't belong to each other: he's an independent and, so am I" (4.52).
Holly won't even allow herself to form ties with a cat. She remains completely isolated from anything that could represent personal attachment.