The new shark girl is pretty neat, and the fact that you can unlock her midway through the game makes her useful. However, her addition, and the fact that she is going to be used between the (current) mid to end game has unfortunately made the game even more grindy. I think it all ultimately boils down to the way XP is granted after winning a battle. The current system where you are awarded with a pool of XP which is then divided among your party, while novel, basically makes it that it is in fact it more efficient to level up your furries independently of each other, instead of bringing them all as a single team. I think that a more traditional XP system, where the rewards are granted independently to each party member and not as fractions of a larger pool would be ultimately a better implementation than what he have right now.
Also, I don't know how it is on her other growth paths, but on the FMG path the shark girl starts with a mana pool so low, that she cannot use any of her skills until she levels up a couple of times.
EDIT: After playing for some more, I gotta say that receiving some extra rewards for feeding Maris could be a good idea, as there's no point to doing so besides making the local sharkgirl BEEG.