Allow several weeks before the intended start. A Canadian citizen can apply at a port of entry on the day of travel, but redrafting the offer, obtaining transcripts and restructuring a contractor arrangement into employment are what consume the calendar.
Preparation sets the date, not the border crossing
The decision at the port is quick; everything that makes it survivable is not. Wendy should count backwards from the start date and allow time for the employer to redraft the support letter, for her university to issue an official transcript, for a lawyer to read the employment agreement, and for the numbered-company retainer to be replaced with a salaried offer. Each of those has a lead time measured in weeks, and the last one may need a second round of negotiation.
If the employer prefers to file Form I-129, add USCIS processing time and remember that she should not travel to begin work before the approval notice exists. Where the U.S. operation has a seasonal deadline, say so in the negotiation and agree a start date that can absorb a delay.
Admission is granted for a period not exceeding three years and is renewable, so build the renewal into the plan from the start.