Confinement Nanny

Hi! May I ask 1. When should we start engaging and book a confinement nanny? I got a recommendation from a gf who just gave birth recently…but instead of hiring the nanny privately, I prefer to engage her through agency still, cos want to have a back up plan/ replacement if we have to replace the first nanny during confinement due to covid or any other reasons. 2. If hire through agency (confinement angels in this case), am I able to choose a particular nanny? Thanks! Will be grateful for any advice:)