Not on TD status. TD dependants may live in the United States and may study, but they are not authorised to work, and no employer letter changes that.
TD is residence and study, never employment
Hypothetical example: A spouse admitted in TD status may accompany the principal and may enrol in study, which the immigration authorities list expressly among the classes permitted to study. Employment is a separate matter. TD carries no work authorisation and there is no application that converts it into one; the spouse who wants to work must qualify in their own right, whether that is a TN of their own, an employer-sponsored classification or something else entirely.
This has a practical consequence for a farm household where the second income is real. If the spouse manages the books for a Canadian business, whether that work may continue from a United States address is a question to raise specifically, because performing services while physically present in the United States is not automatically outside the rules. Ask before assuming, and ask before the move rather than after.