How do you know what is best? You try them, that's how

. If you can find a place that has different releases that she can try that is the best way.
The companies I listed all make very good releases though, it would boil down to what felt good to her. But the short head will help with little hands and a short draw length.
Copper John also makes a release that is a hand held, but has a wrist strap. And the trigger is in the grip under your middle fingers.
I also like the carter lockjaw, quickie and the two shot. The fletcher Jim Dandy release would work well too. And I like the TRU ball short and sweet.
You can look at all of them at Lancaster Archery.
Paul