If you'd like to write some fanfiction in which Althea and friends explore one of these topics, I'd love to include it as a "bonus chapter" here on the website. (It would need to be age-appropriate for ages 10 to 14.)
Here's a list of the topics left out of the published story:
Calc I:
Limits (usually a whole chapter) & Continuity (Coming soon: bonus chapter on definition of limit)
Related rates
Differentials
Mean Value Theorem
L’hopital’s rule
Integrals of Inverse Trig Functions
Calc II:
Volumes by ‘shell method’
Applications: Center of Mass, Work, Hydrostatic Pressure
Techniques: Integration by Parts, Partial Fractions
Simpson’s method
much of Infinite Series
Parametric functions & polar coordinates
If you want to learn all that, there are many good (free) textbooks online. Among them: OpenStax (conventional), Boelkins (project-oriented series, may not have complete proofs). MyOpenMath is a (free) online homework system. In Calc III, with three dimensions and multiple variables, the connections to physics become more visible. It’s hard work to learn and it’s beautiful.