Yes she definitely is. I am the principal applicant and my wife is a dependant applicant, she has to fill her own IMM 5406 form and sign it as an applicant of this form.
Who needs to fill out this application form?
This form must be completed by:
You, as the principal applicant,
Your spouse or common-law partner (whether accompanying you to Canada or not), and
Your dependent children aged 18 or over (whether accompanying you to Canada or not).
SECTION A
Write the personal details for:
yourself,
your spouse or common-law partner, (if applicable)
your mother, and
your father.
From another thread:
"You filled out one with you as the applicant, and now your wife completes another one as the applicant (nowhere on the form does it say principle applicant, it just says applicant.)"
