Your Mum should understand what you are asking at the time she is asked. She does not have to remember what was discussed 10 mins later.
Anyone within reason can be the certificate provider, it does not have to be a professional. It could be a neighbour, a friend, or your mums hairdresser, provided they have known your Mum well for a period of time.
Normally, if you ask your Mum in simple terms does she wish you to look after her finances if she cannot look after them, and this is done in the presence of the certificate provider, then this is all you need. Obviously you need to discuss with anyone else who has an interest and they can be named on the form, and notified of its lodging.
Assuming you have no one who is going to question you being appointed as PoA, then it should still be a fairly simple process.
We did not get both PoA for Mum until after she had been diagnosed with Dementia. I asked a neighbour, a professional, who had lived next to Mum for 30 years to come in with me, and we all had a conversation where he just asked Mum if she wanted me to look after her money and property for her if she could no longer manage, and if she became ill did she want me to speak to Doctors on her behalf to make decisions on her treatment.
Mum was fully aware of what was being discussed during the time we were with her, but she would have forgotten the conversation 20 minutes later. The neighbour was then happy to act as certificate provider.