ILR 5-year 43 days short of 60 months

Hello,

I am British and my wife is Mexican. She first lived in the UK under a Tier-4 student visa from Sep 2012 to May 2014. After we got married, we applied for her first 2.5-year spouse visa (from within the UK) which ran from 22nd May 2014 to 22nd Nov 2016. As we were to be out of the country from Oct-Dec 2016 we then applied for the second 2.5-year visa in Sep 2016, through the premium service. The second visa therefore runs from 12th Sep 2016 to 9th April 2019.

This means that when her current visa expires on 9th April 2019, she will be 43 days short of the 60-month continuous residency requirement for the Indefinite Leave to Remain (even though she will have actually lived in the UK for almost 7 years). Reading through the forums it seems we can apply for the ILR from 24th April 2019 (28 days before the 60-months). This means we are 15 days short.

Reading through the immigration rules, it seems like she should have been given an extra 28 days on her current visa, as she had more than this amount left on her first visa. This would have solved our problem, but we are guessing its more trouble than it's worth to try to rectify this now.

What are our options? As I understand it, we could:
1. Extend her existing visa via FLR(M) and apply for ILR once eligible, wasting a thousand pounds or so in the process
2. Apply for ILR via post and hope that by the time the HO assess it, she is then eligible
3. Apply for ILR via post prior to 9th April, wait until 24th April 2019 and request an upgrade to the premium service - this would be our preferred option if possible as we don't like the idea of waiting 6 months or so without her passport

Which of these is the most feasible, and do we have any other options? Like others on the forum, we didn't realise the problems that would be caused by applying early back in 2016.

We would appreciate any help anyone can provide!

Many thanks