Reddit reviews Mindful Kids: 50 Mindfulness Activities for Kindness , Focus and Calm

You might check out the book "The Highly Sensitive Child" - more info about it here. Not sure how much it will address the question of processing things externally vs. internally, but it might shed some light on her emotionality more broadly.

It might also be helpful to work on emotional literacy with her in general, at times when she's not already activated. There are lots of great picture books to help kids practice verbalizing and regulating their emotions. You might check out Visiting Feelings, The Color Monster, Today I Feel Silly, or My Many Colored Days for some good emotional vocabulary. You might also check out the "When I Feel..." series (When I Feel Sad, When I Feel Worried, etc) which do a good job of showing different ways to handle each emotion. For anger, also try Anh's Anger and its sequel Steps and Stones, or When Miles Got Mad. Each of these introduces different coping skills she can practice to handle her own feelings - when she starts to get angry, for example, you can ask if she wants to try breathing like Anh or talk about why she's angry like Miles.

Another thing to consider is that she might do better processing things in non-verbal ways, such as through art or movement. Another good story, aimed at slightly older kids, is Moody Cow Meditates - which features the brilliant "mind jar", aka calm-down jar. See these instructions (and some cool variations) for making your own (definitely recommend using a plastic bottle rather than glass jar!). The idea is you shake up the jar/bottle to get all those big feelings out, and then sit quietly watching until all the glitter settles. I also recently discovered a cool coloring book that teaches different emotion regulation strategies, loosely based on some guided meditations for kids. There's also a great book called Breathe Like a Bear that introduces a variety of kid-friendly mindfulness exercises, and a cool deck of cards called Mindful Kids. And lots of similar things in app form as well, such as "Stop Breathe & Think for Kids" and "DreamyKid".

Hopefully something in there is helpful!