ILR for PBS Partner: ILR or extension ?

Hello,

I received my ILR- Set (o) (Tier 2 general 5 year route) in September 2019.

My wife's current BRP (Tier 2 Partner) expires on 04.09.2020
Her first Tier 2 Partner visa was issued on ..... .04.09.2015
Her date of entry .................................... 06.10.2015

During her first 12 months (04.09.2015 - 04.09.2016) she had 187 days of absences, if counted from the date of issue.

ILR guidance says "you must calculate the relevant qualifying period by counting backward from whichever of the following is the most beneficial to the applicant:
- the date of app
- the date of decision (what is this?)
- any date up to 28 days after the date of application

Q1: Can she apply for ILR to qualify for 5 years closer to the date of entry? I.e. Application date 01.09.2020 (28 days before qualifying date) where absences will be below 180 days, even though visa expires on 04.09.2020?

Q2: there are almost no documents with her no name on it during the first 5 months (Oct 15 - Feb 16 i.e. council tax, utilities etc), as she was going back and forth, except for police registration (OVRO and local police for an additional change of address). Is this a problem?

Q3: Shall we rather apply for an extension?

thanks in advance!

PBS dependants qualifying period for ILR is counted from visa issue date.
PBS dependants do NOT have an absence limit during a visa period if it was issued before 11 Jan 2018
You need to show cohabitation documents for the last two years only

thanks Zimba!