Ok, technically Marena can't do this - using Hybrid Body Rearrangement to bring out the plus-size mutations on her fox form should, at best, result in a vixen the size of a largeish dog. But this is cooler.

What they've actually done is not represented by the rules either, per se, but it should be an effective tactic. It overcomes the limitations on Charm use: one person moves for them all, one defends for them all, and one attacks.