The 22-year-old has the username @natwest on Twitter and has received numerous complaints for NatWest customers who assume she runs the bank's official account.
Miss Westerman's Twitter biography says "I am a 22 year old woman and I'm not a bank" but that hasn't stopped users of the social network from angry NatWest customers hit by the computer problem that has now entered its seventh day.
Many NatWest customers have been left unable to access internet banking, with money disappearing from bank accounts or not being paid in. Miss Westerman has greeted their often abusive Twitter messages with good humour.
She tweeted: "I've never felt so popular in my life. I am a person called nat west not a bank." Miss Westerman has been directing customers to NatWest's official Twitter account, @natwest_help.
Her new-found fame has left her bemused. Earlier today she wrote: "Someone just came to my front door asking for an interview."
Miss Westerman said: "My friends find it hilarious when I tell them about all the messages I have received."
She added: "I am a teacher and when I recently told the children about what had happened they found it very funny."
She said that she did not want to change her Twitter username because she has friends abroad that she would not want to lose touch with.
NatWest has more than 7.5 million personal banking customers but it remains unclear how many have been affected. More than 1,000 NatWest branches were opening their doors from 8am to 7pm today as staff seek to resolve the problems.
The computer software problem started on Tuesday night and reportedly arose following an attempt to install a software update on RBS's payment processing system, which was then corrupted. The group has said the issue had now been fixed.
Misunderstandings over Twitter names are not uncommon. Last year, a woman from Massachusetts who uses the Twitter name @theashes found herself on the receiving end of a barrage of tweets about the cricket series.
Ashley Kerekes, whose following on the social network swelled to more than 10,000 thanks to mistaken cricket fans, was eventually flown to Sydney by an Australian airline to watch the fifth Test.
