Mental gymnastics aren't required. Dolly never spoke at length on the topic, so no one can really say that she had deep-dived into it, understood both sides, and chose gender ideology. You want to believe that, but you're just projecting it onto her attempts to be kind.
Dolly was in the last years of her life. She had health struggles to contend with. It's not condescending to assume "poor, silly old Dolly" just didn't have the time or energy to get into it. The reality is that she was 80 years old and had had more immediate concerns. She couldn't give the trans debate the attention it required. If there was an 80 year old woman in my life who was in and out of hospital and still trying to keep working, I would not expect her to also be fully informed on the trans debate. That's insane.
All we can do is try to work out how she might have come down on the issue, based on her past actions and beliefs. I don't believe she would have been a ra-ra TRA, if she saw what the ideology was doing to women. That's not mental gymnastics, it's an objective assessment of her character. You seem to think that because Dolly was compassionate to trans people, she would have written off the concerns of women the way you do. I'm not convinced.
By the way, you don't have to have a "superior intellect" to question gender identity. All you have to do is be shown the stories of the people who have been hurt by it. You listen to them and allow yourself to think "Is this wrong?" You listen to the totally illogical arguments of the TRAs and allow yourself to think, "Does this actually make sense, though?" That's it. They're pretty simple thoughts that don't require MENSA levels of genius. You just have to give yourself permission to use your own brain, which most people are terrified to do, because there's a societal cost to admitting this is all harmful bullshit.
Of course, if you're someone who transitioned, or transitioned your own child, the cognitive dissonance is what's terrifying. Whether you believe me or not, I really do pity those people. That's a horrendous thing to live with and have to try and outrun mentally for the rest of your life.