Your doctor will need to apply for PHAC. If you are having a normal pregnancy many doctors will not fill out PHAC because that is not the intention of the PHAC program. PHAC does not add any benefit for normal pregnancy. If anything it will cause you problems because visas tend to be authorized to leave soon and to remain in Canada for a short amount of time. PHAC is really for emergency situations that are time sensitive like a funeral, an emergency hospitalization like a serious heart attack or large stroke and for situations where family are near death and people are trying to rush to Canada to say their goodbyes. Apply for a new TRV and follow the directions for travellers who are travel exempt so that your application is prioritized. Your mother can not quarantine in your home unless you have a separate basement suite because pregnant women and infants are considered vulnerable to covid and also usually have contact with the health system. You’re applying to travel in the future so there may be many changes in entry requirements and quarantine by then.