Under section 6 in the application for proof of citizenship (CIT-0001), it asks if the parent acquired another nationality, followed by what country, on what date and how it was acquired; but it does not ask you to send in proof of the acquisition. So this is not true.You also need to prove how exactly did she get her USA citizenship...
Why would Wyfarer have to prove to the government that her mother renounced her British Subject status, if he/she is trying to get proof of citizenship because of his/her mother? Sorry, but that does not make any sense; it's almost like self-incrimination. The British government would have recorded any renunciation, and it would show up when IRCC is researching/processing Wyfarer's application because Canada and the UK share informationprove...if ever she rejected to be a British subject in the past.
Wyfarer is correct in that he/she just needs to follow the checklist for scenario 3, which are certified copies of his/her birth certificate, mother's birth certificate, and regular copies of two pieces of identification with one including a photo, receipt for payment of the application fee, and 2 citizenship photos according to specifications.