It's over kill but it's a great idea. I have never seen or heard of the life jacket but I love it. As long as your sister cannot come into possession of the firearm she will be OK. It's your firearm and the law cannot punish you because of your sisters past. Keep the firearm secured at all times.
As JK stated, its a good idea to check with the parole/probation officer or call your police department and ask to speak with someone in the firearms unit.

