2-factor verification for client proofing

I wonder if you could set up a special email address against this Adobe account, which you could monitor so as to gain access to it yourself. Then set an auto-forward for this email address so that your client will immediately receive a copy of the emailed authentication code when necessary. When some different client needed to later use this same Adobe account instead you would ensure it was signed out. change the access password, and alter the auto-forwarding setting for the associated email account so that this different client will receive the authentication code in their turn.

But I would generally agree, far easier and simpler to just have the client make (or else use if they already have) their own Adobe account entering whatever email address they like. Then for any difficulties the client did have with signing in, they could turn to Adobe help resources rather than needing you to provide technical support.