The best way I can start a reply to you and Koolau is by quoting part of my post - "It isn't fun, but I have the best relationship with her I've had in decades."
Honestly, one of the biggest challenges on my side of this relationship is in how to set aside judgements based on how DW and I approach our lives. My sister is wired very differently from me, and it caused friction, jealousy, and resentment to be a factor since we became adults. Four decades later I've mellowed, and she has the best mental health of her life. Staying in the Trustee role is part of how I can support her and feed our relationship. Prior to mom's passing, I fully expected my sister to demand her portion of the estate ASAP and we'd never talk again. I'm grateful for this turn of events.
The good reason for not taking the distribution? She and her now ex-husband had been self employed their whole time together. They owed substantial amounts to the IRS at the time of our mother's passing. So She's waiting for that debt to be declared uncollectible. That certainly isn't a path I'd walk, but it's her choice.
Here's a chance for a PSA - If you know anyone who is self employed, see if you can get them to really consider the long term impact of manipulating their income to minimize Social Security and SEP payments each year. My sister will likely get around half of what her cohort will once she starts taking Social Security. And sadly she's constantly tempted to take SS before FRA.
Finally I didn't know much about Trusts when this all began, so I'm very thankful the attorneys who've advised us created the most flexibility for the Trustees.
Kind regards,
Chris