As previously ruled vHarmony has to absorb all of a single instance of damage.
Following discussions with the design team she is unable to transfer any more instances of damage after she has been reduced to zero HP (i.e. she gets to ignore the remainder of the dmg that kills her, but any subsequent dmg she can't take).
For Attacks and Character Plays work through the relevant timing sequence for each model affected and transfer damage as it arises.
For Traits and other types of Plays, although the damage is deemed to be simultaneous, resolve each instance one model at a time in the order of the active player's choosing and transfer the damage via Team Player if desired.
When resolving condition damage in the End Phase, resolve all conditions on a single model, apply the damage and transfer via Team Player before resolving all conditions on the next model.
For example, vHarmony has 5hp remaining, and Smoke declares Chemical Shower. There are 3 enemy models within 6" of Smoke suffering the burning condition. The Masons player may only choose two of the three instances of 3 damage to transfer to vHarmony as once she reaches 0hp she can no longer choose to suffer damage.
If vHarmony is one of the three players in range, she will always suffer that damage, so the Alchemist player, choosing order of resolution, should probably choose to affect her first.
Reopening thread for any follow up questions.