Despite noticing that Sofia was fiddling with her finger and deducing that it might be missing a ring, Livia had no suspicions that she might be hiding what Mary Flaherty claimed was her diamond. Why should she? However, if Sofia had been flashing a brand new diamond ring, Livia might well have twigged.
Fortunately for Paolo, Sofia was smart enough not to trust Livia and certainly not to show anything off that might draw attention or envy. Unfortunately Paolo didn’t get to know this.
He called Sofia, found out she’d just met Livia, and from then on, was bricking it.