The only "authority" is CTSHK. Their information is here: http://www.ctshk.com/zhengjian/gangao.htm

If she had a HRP at one time, it's a lot simpler. Just the old document is good enough.

If she's a first time applicant, proof of Chinese nationality is required. An HKID is not good enough. The proof will normally be a HKSAR passport. This way the HK Government will confirm her Chinese nationality (which should be easy) and CTSHK will issue the HRP.

She can apply for the HKSAR passport in Canada at the Chinese embassy/consulates. HRP application can only be handled in HK.