It’s not an exact 60-month process... the date the visas are valid for will depend on when you applied, and when they were issued.
As long as the FLR(M) is valid long enough for her to apply for ILR before it expires, it doesn’t really matter what the end date is on it.
She has been lucky and has been granted her visa for longer than she needs it, which gives her more leeway to apply for ILR in 2021.
If she entered the U.K. on 15th October 2016, then she can apply for ILR as early as 17th September 2021.
And because her visa is valid until 5th November, she has until 5th November to get her application in, instead of only having until 15th October.
So, this is a good thing and nothing to worry about at all.
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