To set up an online account, the IRS does require some basic US financial account information to do a soft inquiry for verification.  If your client doesn't have any, my understanding is that there is no way she will be able to register for an account.

If all she needs some basic information about her return, she could call the IRS.  If she needs a transcript or copy of her tax return, she could call the IRS, submit a 4506 series form by mail, or authorize you to access her records/represent her.