In general, if you want to do refresh-switching, that's what Modular Abilities is for. Frequent switching of stunts and/or powers is tremendously powerful due to massive flexibility, so you have to pay a -2 refresh surcharge to do so.
That said, one-off switching is something I'd be ok with, so long as it was appropriately rare and justified by the character. This case, where a player is taking a stunt as a "precursor power," is in my opinion one of the best situations to justify switching. She should make sure the table and the GM were ok with it, but I would support her case while noting that this was not an open invitation to edit your refresh list between sessions.