this is an interesting one, prufrock. was her depression "situational", i.e. caused by bereavement or other external factor? has she been going for counselling and is her graduated return to work making allowances for the fact she may wish to continue with counselling? have you spoken to her about her expectations/desires/objectives for returning to work?
it is not absolutely clear from your post, but i am assuming you are her boss? if so, when she returns i would sit her down and have the most honest chat you can with her about what she feels up to doing. perhaps you could stress that you don't want to treat her with kid gloves, but that realism must prevail. i would use the analogy of a physical illness on this, e.g. "if you had broken your leg, no-one would expect you to etc etc ..."
are there any "shared services" roles in your dept. (e.g. reconciliations, accounting, admin) which do not involve direct contact with clients? perhaps she could do something like this until she has found her feet?
i think you and your firm are already treating her differently, in that she has a gradual return to work and that you have reorganised the work of the team in order to shield her. i'm sure this is the commonsense solution given what happened before, but perhaps it would be best not to insist that all is as it was... i assume she is depressed rather than stupid!
thinking about it, the mindset of comparing her experience to a physical illness might help everyone get the right perspective on the situation.
when is she due back?