I think this is more her unlocking her divine or supreme divine skill. She is slowly drawing more of it out and gaining more strength. Before this point she was using the bare minimum of her true power. Now she is slowly drawing more out because she is acting out of love for others.
Problem is the flow of these two chapters. (Actually three. Chapter 21 also had her struggling.)
She struggles against an even opponent. She overwhelms a clearly inferior opponent.
There is no transition aside from that last panel in the previous chapter that shows her activating her skill.
Nothing in the story has shown her being a slow-starter. Nothing about her skill needing activation conditions or build-up.
The whole previous chapter is her struggling against what is actually a much inferior opponent. So it's just there to build false tension. Some mangas give "build-up" abilities to their characters so they can struggle and there is tension as the character in question attempts to stay alive long enough for his skill to get ready. But nothing hints that it's the case here. She just got beaten up for no reason, as she's never been shown to be the type to enjoy fights either... in fact she's been established as the exact opposite. Someone who hates fighting, but does it reluctantly to reduce her overtime work and does it as quickly as possible because this too is overtime.
So the whole previous two chapters are a complete contradiction to either every chapter that preceded them or the one that followed them.
Going from chapter 20 straight to chapter 23 would actually work better in terms of consistency. The tension already existed in the form of "will she be on time to save Mr Tank?". Adding the two chapters of "even fight" sequence breaks the flow for cheap additional tension that prove completely artificial in chapter 23.
Or go the opposite direction and make Mr Demon God a true opponent on equal grounds. Show that there are actual threats out there that even the one-punch receptionist struggles with. Other than overtime, that is.
(Edit: then again, you can also establish that her Divine Skill is a build-up type. This can work, but must be done or at the very least hinted at.)