She cannot manage it from inside the United States. TD status allows residence and study but not employment, and managing an Ontario business from a U.S. home is U.S. work regardless of where the income is taxed.
Decide where the management work will physically happen
The distinction that matters is location of activity, not location of the business or the bank account. Answering booking enquiries, directing cleaners and handling guest problems from a Maine kitchen table is work performed in the United States. There are three realistic responses. She can hand day-to-day management to a Canadian property manager and remain a passive owner, which is generally compatible with TD. She can plan to do the work only during periods when she is physically in Ontario, which requires discipline and a truthful record. Or she can look for a route of her own, such as her own TN if she qualifies in a listed profession. What she should not do is assume the activity is invisible because the money never touches a U.S. account. The employer's relocation help does not extend her permissions either.
Hypothetical example: a dependent spouse owns a small online quilting-pattern business and plans to answer customer messages from the American home. The first review should separate passive ownership from the work of designing patterns, marketing them and responding to buyers. A written handoff to a Canadian contractor, along with account-access records, is more useful than a promise to work only occasionally. Sequence the decision before moving: either suspend the active work while present in the United States or obtain independent work authorization. Calling the payments Canadian income does not decide where the labour occurred.