Check with the CPF Board on this. CPF's Web site generally reflects current rules, not necessarily those that apply to every case (particularly older cohorts).
The Standard Plan debuted on January 1, 2013. During the first year (2013) it was also available to existing CPF LIFE participants who wished to switch to the Standard Plan. Under the "OG" Standard Plan mechanics there were (typically) two premium deductions:
1. At age 55, equal to the Basic Retirement Sum (at that time).
2. A couple months before age 65.
Nowadays there's only one premium deduction, just before payout start.
So I think the question for the CPF Board is "What happens if I die before payout start? In particular, what happens with the first premium deduction?" I'm assuming the second premium deduction hasn't occurred yet, and that seems like a reasonable assumption if her RA has some dollars in it now. And there are two possible answers: (1) The BRS is returned (without interest) to her CPF nominee(s); (2) The BRS plus interest is returned to her CPF nominee(s). If it's (2), great. If it's (1), less great, but there's still that second premium (that's clocking interest) that hasn't been deducted. So it could still make "sense" (as defined in this question) to defer to age 70 if that second premium won't be deducted until then.
Another, related option I suppose is to do that (defer payouts) if the second premium isn't deducted until around age 69 years 10 months, then make a property pledge, then withdraw the entire remaining RA before payouts start. That'll of course reduce CPF LIFE payouts (and rather dramatically so), and it'll eliminate all RA interest earning thereafter since the dollars are obviously no longer in RA. (Maybe they end up in a 0.5% interest earning bank account?) But it would certainly reduce interest "loss" to the pool for early death dates. So there you go, that's another possible option I suppose.