Possibly, if a U.S. entity has prearranged her professional services under a written engagement and she is not in substance self-employed there. She must be a Canadian citizen, and Accountant is a listed profession met by a CPA designation or an accounting degree.
What to ask the client and the firm
Ask the manufacturer whether it will issue a letter confirming it has engaged her professional accounting services for a defined period, and whether it prefers to hire her directly. Ask her firm whether a written secondment or services agreement will exist, what it says about supervision and deliverables, and whether the firm's other partners agree to her absence. Then look at her ownership: a minority partner seconded under a firm agreement is a different picture from a sole practitioner invoicing a U.S.
client from a U.S. desk, and the second picture is self-employment, which TN does not allow. The duties must be accounting work matching the profession; a controller who spends most of her week supervising warehouse staff is not doing the listed job.
Citizenship is absolute. If she holds Canadian permanent residence rather than citizenship, TN is unavailable regardless of how the engagement is structured, and the review should say so at the outset.