SORRY NOT A FICUS BENJAMINA

Ficus benjamina I know, Ficus Danielle I don't - are you referring to a houseplant and is it similar to benjamina? If you are, it'll be the change in the weather, even if its in the house - they are extremely sensitive to temperature change and, in particular, draught, even a small one, and will drop leaves if they're upset. Don't worry about it, they do drop some leaves all the time anyway. Check its not infested with anything, keep it watered and it will recover once its accepted whatever change its reacting to - you may have to remove some of the defoliated branches if they're that bad. The plant may think its autumn - I find mine sulks a bit as the seasons change and may drop more leaves than usual, even though its in my sitting room.

Danielle is a cultivar and like the benjamina it will not like change. Changes in light intensity, changes in seasons or being too close to drafts will often cause leaves to fall. It's a reaction to a change of some sort.