Can she threemerge them or does she have to go pairwise? 

Assuming it's pairwise, she's going to start by shoving together the energy booster and the regeneration power first.

It is, in fact, not pairwise! The three powers click together just as easily as before, forming a gestalt power that speeds up regeneration by supplying additional biochemical energy and extrapolating how the biology is going to adapt in response soas to anticipate future energy needs.

Sheeeee no longer has any idea how the merging works. She needs to figure that out. 

Okay, back away slowly from the really cool accidental power, she is messing with stuff she does not understand. She'll keep applying her present changes but that's it for now.