Best way to draw-down ~2.5% annually

I'm helping my mother with her finances. She's in her early 70s and not looking like she'll slow down anytime soon (with some 100+ longevity in her genes). She's set up pretty well, such that she only needs to draw about 2.5% of her portfolio, to cover her financial needs (after CPP, OAS, and pensions).

Right now, her investments are somewhat diversified, except for a significant chunk in a single big5 bank (inherited from her parents, and has been a good performer for generations, so there's a sentimental attachment). She draws the minimum required from RRIF every January, and contributed the max to TFSA at the same time, with cash needs being drawn from unregistered investments.

I've been talking with her a lot lately about moving everything to a simpler all-in ETF, and considering her low draw-down needs, we're looking at slightly more aggressive strategies than some might choose at her stage of life (higher mix of equities).

I'm an accountant, but not a tax accountant, so I'm hoping someone can share some strategies for effective ways to manage the draw-down phase of a portfolio, when the generally assumed safe withdrawal rate of 4% isn't needed to meet cashflow needs.

She isn't all that averse to paying taxes, but I'm sure he won't complain if I can save her a bit of money there. Given that she has more than enough to continue her preferred lifestyle, her primary interest is in leaving as much of an inheritance as she can.

Any advice or discussion would be greatly appreciated.