Your bigger challenge will be that your father did not declare her
Section 117(9)(d) clearly states that undeclared and un-examined spouses and dependents are not sponsorable as members of the family class. By not declaring his child, your father has closed off an avenue of investigation into his admissibility to Canada. The consequence is that he has probably lost forever the opportunity to sponsor his child.
There has been a pilot program launched by CIC for undeclared dependants
https://www.canada.ca/en/immigration-refugees-citizenship/news/notices/sponsorship-undeclared-family-members.html but if you have been told you would qualify for it, then you have been misinformed as it is for a very specific group. If you have not yet, I would enlist the legal help on this.