[pleboidal]

Takes her out of the game. The pills don't produce a conclusive casualty in under an hour. She might survive by incidentally vomiting, recover and fly home. There might be others, undercover, tailing the kidnapping, and waiting to rescue. Rescue might simply be incidental first responders. Since she wasn't rescued we might assess there were more layers of interference in the murder. Lookouts, participating as accomplices.

The burning kills quickly (minutes or less of smoke inhalation), and even if ineffective in killing due to interruptions, certainly produces scars that won't be easily hidden in the future and puts someone on the sidelines.

It also sends an unpleasant message to everyone who didn't bring her home, and we still don't know who that is. Given that she wasn't even recovered, one might presume her original identity was marked deceased in a contrived accident, conincidentally, thousands of miles away. Maybe her family already knows the real story, and remains quiet.