I’m not quite sure how her ability works, with regards to additional actions.

Does this prevent only cards which say have an additional action? Or can it be used to stop things like ambush actions or multiple chaining of activating characters, like commando droids?

any help on this will be greatly appreciated

Only ambush and additional actions does works with iden's. It's said that after you activate droid character, you may activate another droid or support. That's 1 action, the after effects are completely different from an action. Iden can't stop the after effects, only ambush and additional actions.

@hurricat5 That’s excellent thanks very much