Private User Editable Forms

Have an interesting request from a client. She is a doctor and wants to be able to offer her clients a private online form that they can use to keep a food diary over the period of a week.

What this means in practical terms is a private page (unique password) containing a form which contains saved data that the user can add to or edit during the week they are monitoring their diet.

I have looked at Wiki or editable front end input form plugins but haven’t found anything suitable.

Would really appreciate any suggestions.

Thanks!