Just finished watching pal that was a belter! Ok here is how it happened on Moon princess. You get 3 of one princess and an odd one that is an instant trinity.
So say you got storm storm love love in the line that is 2 sections filled say you get star,star,star and love thats a trinity. This is because you have hit 3 princesses and 4 princesses in one spin. 🙂 It’s my favourite way of landing one because it’s spawny.
The other q you had I can also explain storm is fickle she doesn’t normally take away more than 3 princess symbols so yes she can take away the green one and be nice but she can also be a cow and take away the wrong ones leaving one princess.