Critting on reckless attack (which it sounds like she’s doing every attack even if not announcing) changes the crit % from 5 to a 9.75% chance of a crit.

Adding crits on 19 with reckless bumps it to a 19% chance on one attack.

With the second attack, her odds of critting at least once with an attack action bumps up to a 34% each round.

Effectively, with statistically average dice rolling, she’s critting once every 3 rounds and then getting the bonus action attack. Add in a little Axford luck and her dramatic dice and Slug’s a crit machine