Your mother should not have online banking, she is not up to it.  Help her take anything off the computer that could
lead to her accounts and identity being stolen.  This is a sad situation, I suppose her email is important, but this is not
good, she is too trusting.  It will be very hard to explain to her, it may be time for her to let you help with banking with
a power of attorney, and control.  
It was mentioned credit bureau's, that would not help with a fraudster, those guys are not checking her credit rating........
before stealing her money...lol.
I would restrict her banking to a small account at the bank, and that is all.  The rest needs protection, and it seems she
now understands that.
I used to be a banker, and I don't have online banking.....and never will.