Hmmm … I’m not sure that the story is actually saying that, but it’s difficult because we’re talking about the MC throughline rather than the whole story. Maybe I’m encoding it inartfully. So allow me to express it differently and maybe contradict myself
According to Dramatica, if Belle is a Be-er, she can’t be in Universe. I don’t see anything that suggests she’s a Do-er rather than a Be-er. She complains, but takes no action to change her environment or escape it. She escapes internally into books and imagination.
By contrast, the Beast seems to be entirely focused on his external situation, and controlling the environment (keeping people out, threatening people, imprisoning people, etc.). When she reads to the Beast it’s actually moment of bonding for them – and is a step toward him taking on more of her Be-er approach (looking inward) and changing.
So from a storyform perspective, I think that it’s arguing that as a Be-er, if you hold out against the controlling and/or provincial Do-ers in your world who are trying to change/control you, you’ll have success and maybe even turn your Beast into a prince. Or to put it another way, don’t be swayed from who you are (Fixed Attitude).