Hi homie ! I think that it can be a lot of thing slowing her down at that stage. 1st it could be a little over watering, you can use the lift pot technique (hit me for more explanations). 2nd It could just be a genetic issue : this plant is just weaker than the others. 3rd It could be a ph issue that slow her down : check your ph , if it's not between 6.0 and 6.5 correct it (you can start at 5.5 for seedling and then slowly up it to 6.0).
But your plants looks like clones so maybe that cloned is simply not well rooted so it is now hard for her to recover lost time (but you can give her Rhizo longer than the others). I hope it will help you 👍👊😁