The way the menu is designed and the fact that each level has a tutorial pop-up implies that the levels can be played in any order, but ghost is so far out of line with the other two that i'm genuinly unsure if that is intentional or not. Secondly, Ghost has 2 seemingly unrelated gimick. Assuming she is designed to be the hard, simple expanding on her deceptive throwing technique would make significantly more sense then just arbitrarily extending the boss fight length.
Finaly, I feel that the RNG of ghost's dodge needs to be normalised or eliminated. As far as I can tell, it is fairly easy for a player to beat her by getting lucky or fail to beat her by getting unlucky. As it stands now she just feels bad to fight.