Murder a nun - when you absolutely, positively cannot be bothered to wait in line to get into hell.
I’m going to venture a guess here but I’d start looking into people she helped recently and see if anyone knows whether she kept a stash of money in her apartment anywhere and whether that info was public knowledge or not...
This is not a venial sin nor a mortal sin. This is a cardinal sin. St. Peter won’t even talk to you at the Gate. You go directly to hell.
May the Sisters find peace.