It is too complex. When you are working on any scene, you have one amorphous blob - player. When you are working with Bess, you have two of them interacting.
Well, it could be done, but it still would work as a biped. Technically, it IS biped, just with unusual body/legs length ratio. And it would require some dirty hack since there is no torso type.
Smooth transitioning requires a lot of checks to make sure it is really smooth. Like...
And what if you have bunny/bear tail? "shrinks" won't work. So it is better to make sure it would work for all shapes.
Missed that edit... Quadripedal. Those bipedal bird taur things won't work well...
Heh, funny thing - it only requires "fluffy" skin flag, but not fur itself. Not sure if it is a bug or not. But DracoGuard is clearing skin flags with changing skin type. As many other TFs do.
Better make her a male who got a vagina and trying to get rid of it (or deal with it). FtH is much more common story than MtH, after all. Maybe a trap who tried to trick a wrong person.
Most, but this is not a specific TF, so I am free to choose any option available! Or make something up. After all, birds are not exactly a good material for anthro.