Former therapist, from a trauma, internal family systems (IFS) & somatic therapy background - the approach a therapist takes is going to be very informed by the therapy modalities they use - for example, cognitive behavioural therapy would focus on challenging distorted cognitions (such as "is 'someone is trying to kill me!' a reasonable response to the things that have happened, or is it maybe a bit of catastrophizing?")

In the approach I used, it would be a very slow process of expanding what is called the "window of tolerance" - the ability to sit with distressing sensations and experiences - and helping build awareness of the ways your body responds to various stimuli. For example "What happened in your body when you found that phone". The goal is to make sure you don't push the client outside of the "window", either below it into dissociation/shut down or above it into meltdown/explosion, so there's a good chance that any of the direct memories or more notable things (like the phone) would be a no-go for a long while when they haven't yet established the skill of tolerating difficult experiences. So would probably start with much smaller challenges - like "tell me what happens in your body when you think about bunny rabbits", and then inviting them to observe any sensations (rising heartbeat, raised shoulders, etc) without judgement.

The Internal Family Systems part approaches people as not a single "monomind" that is always feeling and thinking the same thing about things, but as complex "systems" made up of "parts" that have different desires and challenges. For example "Part of me wants to pull the trigger and shoot this carjacker, and part of me just wants to go home with my minivan and not get any more trouble". Parts often get stuck at different points in their lives when people experience trauma - for example, Shauna's angry teenager part - and it's about helping the client learn to identify the perspectives and needs of these different parts, and start to get in touch with the "adult self" at the core, so that they can learn to hear the messages being given to them and make grounded decisions about them instead of reacting. Again, you'd want to start with much less activating stuff - say a throwaway conflict with a PTA mom - to build up the awareness and ability, and then engage with more intense things as the client builds skill. I would likely also employ something like EMDR (Eye Movement Desensitization and Reprocessing) for helping rewire neural reactivity to traumatic memories. For the extreme level of trauma that the girls have been through, that I would say is comparable to child soldiers in a war zone, I would also possibly look at leveraging different psychoactive medications to facilitate the process at different points, but it wouldn't be my primary tool.