
When I first looked at Stella, I worried about being able to trigger her ability reliably with lower difficulty Chaos Bags. Then I fooled myself briefly thinking that her ability wasn't much help except as a bonus to the Survivor "win by losing" strategy (it feels really good to attack an enemy with .18 Derringer, miss, Use Oops! to hit another target reloading the pistol in the process, then shoot the original target with Stella's special action).
Now, while both of those are at least partly true, I'm beginning to see Stella's ability as "tempo protection." While a on a critical test will still ruin her day, Stella gets 3 successful actions in a turn far more often than other investigators. The versatility of that "failure insurance action" allows her to do anything, where most of the investigators with bonus actions (e.g. Ursula Downs, Finn Edwards) are constrained to one sort of action, and Stella is a lot more versatile.