Not three blind men trying to describe an elephant, but two people trying to describe tax withholding without knowing whether the jobs are being worked simultaneously or serially.  Getting back to the question asked:  Who is your client?  If Mom hired you to prepare the return, review it with her.  If daughter hired you to prepare the return, review it with her.  I prepare returns for people all the time who are not clients.  (Usually, they're disabled or incapacitated.)  The name on the return is not always the client.

If your client asks you to review the return with someone else, you may choose to do that. If your client asks you to review the return with both her and someone else, you may choose to do that also, but take that into consideration when setting your fee.  You aren't being paid just for filling out forms, you are being paid for answering questions about the result.