Her position as treasurer/secretary/director of the corporation makes her an employee of the corporation, but not an owner of the corporation. She would have to be a shareholder of the corporation in order to own an interest in it.

Whether she was an interested third party to the transaction and thereby transgressed the law would depend upon the law of the state in which she was commissioned as a notary. Generally, I would prefer to have someone totally unassociated with the parties to the transaction to perform the notarial act. However, it is my understanding that it is a common practice to have corporate notaries notarize the signatures of other employees on documents.

In Connecticut it is not unusual for a law firm to have one of its secretaries or paralegals commissioned as a notary to notarize the signature of an attorney on court pleadings (i.e. affidavits.). As employees of the law firm representing one of the parties to the litigation they are not disinterested third persons. The last time I refied my house (three years ago) the notary that took my acknowledgment on the mortgage worked for the law firm that represented the bank. When an attorney takes a deposition of the opposing party he has to hire a court reporter to type the questions and answers into a transcript. The court reporter is a notary who is empowered to administer oaths and certify the transcript, but he/she is a part time agent (independent contractor but still an agent) of the law firm that hired him/her for a limited purpose.

The requirement for a notarized signature for documents involving land transactions is generally a requirement of the recording statutes in Connecticut. If there is a problem with the notarization that impacts on the recording of the document, it is my understanding that the document is binding as to the signatories to the document. However, it may not be binding on third parties to the transaction that would normally rely on the recording (i.e. priority of claim in a foreclosure). 

The best source for an answer to your question would be the state agency that commissions its notaries. In most states that would be the Secretary  of State.