So, in my previous question I mentioned a human-like race of polymorphs/shapeshifters from biopunkish world of Gaea. Their "normal" appearance (or Huntress' in particular) is not that different from normal human (medium build, darkish skin, about 1,65 m (~5 ft 5 in) tall, short coarse hair, blue eyes)... except for her body mass which is whopping 320 kg (~705,5 lb). Shapeshifting is her trump card in any battle - it's quite disturbing for an enemy when relatively small girl in mere seconds becomes a 3+ meter (~10 feet) tall beast with giant claws and nigh impenetrable scales/fur/whatever situation calls for.
Hence the question: how can I explain this tightly packed body mass?
In case you need any more reference: think Alex Mercer from first [Prototype] game with high "critical mass" level - same body size, way higher than normal body mass.