different relpy address

I have set up my mothers gmail account on the em and when I sent an email to me and replied it elected to sent to a different email address.

Clues for how this may have happened;

  1. On the set up it had this fake email address (which was my mothers first.last@gmail.com), and when sending mail it says that it is sending from this address

Hi Ailsa,
is the correct address the one you are sending from or receiving? Do you have the fake email still set up in eM Client and is it set up as a primary address?
Can you remove it?