It can be, if she applies at a port of entry with a complete packet, because admission in TN classification is decided at that time. It is not realistic if a petition must be adjudicated first.
The route chosen sets the calendar
Hypothetical example: The port-of-entry route is fast in the sense that the decision is made when the applicant presents themselves, but it is unforgiving: everything must be ready, because there is no opportunity to supplement afterwards. The petition route takes as long as adjudication takes, which is not something the employer controls, though premium processing may be available for the form. The variable that most often breaks a short timeline is not the government but the applicant's own documents, particularly a credential evaluation or a transcript that has to be ordered from a registrar. Kiera should also not resign from her Chase position on the assumption of admission; the resignation can follow the decision rather than precede it.
Work backward from the genuine business start date and allow time to collect primary credentials, employer confirmation and any required evaluation. Hypothetical example: Eamon, an urban planner from Canada, has a conference scheduled before a proposed long-term assignment. Entry for the conference does not settle authorization for the later professional work. The employer should choose the work-authorized route before the employee begins duties, not rely on a later change of purpose after arrival.
Keep evidence of the confirmed start date with the packet. A changed start date may require a fresh explanation rather than an assumption that the original timing still controls.