The mission "Financial Offer" will be available after Meimai knights have been destroyed and after Supply Line in the Desert. In order to recruit Anita you will have to perform a 21 hit combo, this can be done using the teamwork attacks. a good combo early in the game is to wait for 2 enemies to line up and attack them with Cassius from the front to get penetration combos and Dragan from the back to knock the one into the other using his hard attack knockback. End the combo with a Battle formation from a third character and you should easily be above 21. Kill the enemies and finish the mission and she will join your party.