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.
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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.
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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
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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