the jahtari being fast, its kinda better having only mage staff so that it can have reach for flying and only has to buff melee, and the ranged isnt usefull with elusive since you bypass guard. The staff is really nice on its own, with the ability to lower mana too, hmmm, and the ranged attack is lower then bows. yet, it IS both kind of attack :S ugh, i guess i'm kinda picky. the only thing the staff of the arcanum has over mage staff is mana drain, just cause the mage staff has reach and lower cost. that and not having to put elusive to bypass guard at a range of 1. Also, ranged of 3 and melee of 4, with the ranged +1 trait of that beastmaster, is the same as melee of 4 with reach.
As a lot of other say, she need some sort of quick ranged attack somehow to really be good at range.
It's kinda late here so maybe my post isn't quite clear (as is my mind right now i guess) but i believe the drawbacks are a lil bit too high for the benefit. It IS a nice idea, but i cant say i'm sold yet.