I think that had to do more with Ariana's availability to actually be there on set…

The thing is though: Sam knew about his dyslexia and had come to terms with it. Ryder didn't know about it and found out because of Finn and Jake. He needed to come to terms with it on a later occasion.

But this episode "didn't air", so Marley actually never got comfortable with doing that. It's an alternate reality where Marley is actually comfortable with doing that.