Your Fiance will only need to send in her Form 1040X to the IRS if the only changes her Amendment shows is an increase in her Standard Deduction (from Single to Head of Household) and her Exemption amount for adding her son.
Basically, only Forms or Schedules that are "changed" need to be included with her Form 1040X She does not need to send in her Form W-2, her 1040, or any of her original tax forms.
