I read of a case involving a Dutch woman in your wife's UK status position who either was separated from her husband or widowed, she has at least one daughter/child who lives in the UK. She asked the Home Office to confirm she would be OK after Brexit, able to remain in the UK at will. She was told her Indefinite Leave to Remain had "expired". It is clear that the Home Office takes the meaning of "Indefinite" to be "undetermined" (not decided) as opposed to "without end".
With full respect for Chris' suggestion, I would not expect any UK authority/institution to keep records, certainly not reliable/accurate ones - they destroyed the Windrush paper records to free up storage space, apparently never thinking to scan them first.
Danny13, why on Earth would she, she already has/had a more useful passport ?