it's the corporation that must file. if you are still a stockholder you would be an owner so if you have her info you could fill it in lines 8 and 9 and then sign the form (see below if you don't have her SSN)
Responsible Party
Any entity with an EIN (the corporation) is required to
report a change in its “responsible party”
on lines 8 and 9 within 60 days of the
change.
Signature
An officer, owner, general partner or LLC
member manager, plan administrator,
fiduciary, or an authorized representative
must sign.
_____
If you are an entity with an EIN and
your responsible party has changed, use
of this form is mandatory. Otherwise, use
of this form is voluntary. You will not be
subject to penalties for failure to file this
form. However, if you fail to provide the
IRS with your current mailing address or
the identity of your responsible party,
you may not receive a notice of
deficiency or a notice of demand for tax.
Despite the failure to receive such
notices, penalties and interest will
continue to accrue on any tax
deficiencies.
__________________
you resigned as president but are you still a stockholder? since you are no longer an officer if you surrendered your shares you are no longer an owner and not the person that should sign the form
_________________________
what i would do if you are still an owner is submit the form filling in her name and for line 9 write "refuses to provide information" if you don't have her SSN