My big concern is that when we trot my Anthem coverage in front of the UK government when Daughter (if it is allowable after Brexit) wants to apply for leave to remain/citizenship they will say it was not adequate as CSI and disqualify her.
Leave to Remain and ILR are UK immigration rules and are nothing to do with those who use EU laws and EU court rulings to be in the UK. Your daughter would have had to use EU rules and apply for a PRC and not ILR as she would not qualify for ILR. But as you know, the UK is leaving the EU by March 2019 and it is unlikely there will still be EU rules in 6 years time, which is the minimum time needed to apply for British citizenship.
I don't think it is worth worrying about using EU free movement rules in 5 or 6 years times, when they most likely won't be there then. You have your link for texts, so that EEA citizens and non-EEA citizens using EU rules/EU court rulings can keep up to date if they won't get British citizineship before Brexit.
A bit a background why the CSI requirement is so vague and why you won’t get a definite answer -
The CSI that the 2004 Directive stated that students, self sufficients, and all their family members must have to be legally in another member state as a qualified person, was never defined. These people can't use that member states health service as a citizen can, meaning they only have to show they have a CSI to be legally on that country under EU rules. If that doesn't cover them fully for healthcare, then they have to pay the difference themselves as that member state won't pay for them.
EEA citizens who retire to another EEA country, have all their health bills paid for by their own EEA country, under the EUs S1 agreement. They get an S1 from their own EEA country and then present that when they want health care in the EEA country they retired to. That EEA country then claims all those health costs back from their own country, via the S1. If they can't get an S1, then they need to pay for all their own health bills in the EEA country they retired to as that country won't pay for them. These retirees come under the self sufficient part of the Directive
Allowing non-EUs family members to use free movement to the EU, came in after this 2004 Directive and only came in because of a European Court of Justice ruling in 2008.
As I said before, the UK still gave free NHS because anyone legally residing in the UK, could use the NHS for free, but they and their family members are still required to have a CSI to be legally in the UK (a self sufficient qualified person or student qualified person) as per the EU Directive on the free movement of people. The UK gave transition for this and enforced the CSI Directive requirement from about 2010.
On 6 April 2015, the UK ended the 'free NHS for all legally residing in the UK' by changing the definition or "ordinary resident" for bill free use of the NHS, under the Immigration Act 2014. If you read that Act, it changed the definition of "ordinary resident" to mean a British Citizen or someone with a valid ILR (Indefinite Leave to remain - which is gained via UK immigration rules).
At the same time the UK linked free healthcare provided by the UK, to those who have a UK state pension. Those who retired to another EU country could now only have an S1 if they are in receipt of a UK state pension. Suddenly, all the others can no longer have a UK S1 and must now take out private insurance (as under the Directive, that EEA country won't pay for them either). They also changed the UK state pension so that this is now only given based on our own contributions to the UK.
At present, the UK is still allowing self sufficient qualified person and student qualified persons, and all their family members, to use the NHS as a Brit who is residing in the UK. This is why a CSI is vague, as the UK doesn't have to do this and could end it.
You can either read other forums and see what they used for a CSI and had their RCs and DCPRs approved on, or apply for your RCs with you as the self sufficient qualified person, with CSIs for you both, and see if UKVI agree they are CSIs.