At what age do you give kids access to their future inheritance if they're pressing for it?

In Arizona. I have a revocable trust and I am the sole trustee. The trust assets are a combination of: 1- assets that are mine, 2- assets that belonged my my late husband. We each had 2 children from prior marriages and all children are included in the trust. My husband passed in 2015 and his assets passed to me, as was his decision after we met with our financial planners. We trusted each other to look out for all the kids long term and it has always been my intention to keep his kids in my trust, along with my own bio kids. The current plan is when I die, they split it 4 ways. In the meantime, I keep an eye on everyone and help out financially when it's smart to do so (i.e. college, weddings). For 9 years, we've been doing great, no issues.

But now, his oldest (30) has been pressing for control of what she sees as "her" share of the trust. (The assets are moderate; not life changing, but a nice security net for all the kids if they're smart). I've explained many times that I'm following her father's wishes and she's better in the long run leaving these resources to grow, but she wants her portion now. She said she wants to control it, make her own decisions. On the upside, she is college educated and has a good job, she is pretty savvy about money in general, although still a bit impulsive. On the down side, I fear she has a greedy, long-term boyfriend and maybe a few other people in her ear about this. She is increasingly frustrated by the situation and I'm starting to hear innuendo during our conversations (i.e. I hope I don't have to see your kids in court someday; the money really is "morally" hers, etc). I really don't want to deal with this and I don't want to ruin our relationship over this. Have I met my responsibility to her and to my late husband by getting her this far? I am considering releasing her share to her now and letting her sink or swim on her own. I don't feel this pressure with my own kids of course (they will definitely have to wait for my death), but obviously things are different in step situations, even when we have good intentions all around. I don't want to spend the next 20 years hearing about how I am keeping what is rightfully hers.

(Legally, she has no recourse, the trust was created following the law with professional attorneys and financial planners. This is just causing a personal issue between us, and I don't want my kids to have to deal with any of this after I'm gone if things continue to sour between us.)

Have others been in this situation? If so, what did you do? Or what would you do?