This is legal by rule 3.4.4 on page 22-23. It meets all of the criteria for going from vertical to horizontal.
Since the catchers are the original bases, only the a, b, and c criteria apply. d and e apply only “when the catchers are not the original bases…”
She does not need a head/shoulders spotter because they are the original bases. There’s also nothing in the rule that says the original bases can’t take steps during the transition.