Try the little more old fashion approach.

Ask the client to print and sign the necessary forms (8879 and equivalent state form.) The can then fax the forms to you, or return them via link, or message you and image. Obviously some of these are less secure than the others, so you need to consider your best professional approach to how to accomplish getting the signatures via some method that works. 

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Thanks for that suggestion George4Tracks. She actually does not have a printer, so this option is unavailable.

Even more old school, perhaps, taking it over there.

But it does not solve the problem for the process not functioning for her. This is what I would truly like to solve.