I don't know if the modding team is in these forums, but here is a bug:
polyjuice_cat.rpy
Line 239
"-Have her drink another one-" if cat_potion_ITEM.owned > 1:
should be
"-Have her drink another one-" if cat_potion_ITEM.owned > 0:
Otherwise means that the choice only triggers if you have TWO or more left. You could also do 'greater than or equal to 1', but I couldn't remember if the symbol was => or >=, so I settled for >0, because it does the same thing.