You may or may not be able to submit 90-day report a week earlier. Sure you can try and nothing to lose by trying to do 90-day report with your extension. The worst thing they say would be "no, come back next week".
All and only foreigners (who with foreign passport (s)) need to submit TDAC. Thai nationals don't.
That means, if she enters Thailand using a Thai passport, she doesn't need to do TDAC. In case she enters Thailand with a UK passport, she needs to submit TDAC with UK passport information.
The banked money to meet the financial requirement for a one-year extension for retirement doesn't have to be international transfers. Just needs to meet the seasoning period for 2 months prior to the application.
International transfer is only for the initial in-country visa application for retirement.
, royal thai embassies and consulate-generals have holiday schedule for each. It may vary even in the same country. Check their website or sns for their holiday calendar.
, Non-O initial visa for retirement/being over 50 also has the same financial requirements as Non-OA (banked 800K baht equivalent or 65K baht equivalent monthly). Most of the other Non-O initial visas have their own financial requirements, too.