She came through the bathroom window

She came in through the bathroom window
Protected by a silver spoon
But now she sucks her thumb and wanders
By the banks of her own lagoon

Didn't anybody tell her?
Didn't anybody see?
Sunday's on the phone to Monday
Tuesday's on the phone to me

The Beatles. Everybody found it made sense. But what did they meant? The silver spoon refers to drugs. Must have an explanation.