Read this accident report.
It states that another male passenger also used an infants life-jacket.
He stated that it seemed small and tight but worked fine.
https://aviation-safety.net/database/record.php?id=20131211-0
Bigger than who?
No mention is made of which man wore a childs life-jacket.
If the jacket is big enough to slip over the head it is unlikely to be tight enough to cause choking.
The jacket is big enough to go over her head but is somehow tight enough to cause constriction around her neck?
Not buying that unless she had a very fat neck.
Image indicates that she did not have a fat neck so how come the 'constriction'.
Why didn't the pilot shout a warning to the passengers to prepare for ditching.
Just before impact he should have shouted for the passengers to 'Brace' for impact/landing.
Official Fuddy N687MA Accident Report
https://reports.aviation-safety.net/2013/20131211-0_C208_N687MA.pdf