Home return permit

Hello, I will be in Hong Kong with my mum, but she will be trying to apply for her first home return permit. She has was born HK, has a HK permanent ID card, but UK passport only. Firstly does she need to apply for a HK passport first?

We will only be in HK for 2 days, so does anyone know if she apply for the permit only. If so, how long do they can keep the permit for as I'm planning to ask someone to collect it, but don't know the dates they'll be coming to HK yet?