Change EU PR card to Settlement card - can we keep PR card?

[obormot]

My non-EU mother (non-visa national - US passport) has Permanent Residence BRC issued under EU rules, and also settled status (attached to this BRC).
She will need to travel to France in the fall, and show that BRC there (for purposes of proving that she was already granted EU residence in another country).
Then she will need to be able to come back to UK in 2021.

If we apply for change to new settlement card, HO link says one has to submit EU BRC with application. But it seems in fact it is not required.
Those of you who went through this process recently, can you please tell me
1) Is there a way to keep EU BRC? (Or should it be submitted with application? Or should it be sent to HO once application is approved? Or once new card is received?)
2A) I understand application is done online, then one tries to get biometrics appointment and to upload supporting documents. And then eventually card should arrive by post (and then sent to EU settlement office to be linked to Settled status)
What are documents required?
Passport, and BRC only? Or also some proof of address? (Utility bill or bank statement)?
Anything else? She was grunted PR in October 2018 and settled status in March 2019.
(We are talking about dependent person over 75)
I need to know in advance to decide what can we do in terms of changing the residence card.
2B) After biometrics are done, it seems she can leave UK, right? (and then family at home can collect new card, deal with attaching it to settled status, and send/bring to her abroad)

I would really appreciate any comments - especially based on recent personal experience.
Than you.