Short answer: it cannot be called safe by default. With complex PTSD and current pregabalin use, only an individualized assessment by a qualified clinician can weigh risks. I cannot verify safety for your friend online.
Pregabalin may blunt or alter psychedelic effects. This can tempt dose increases, which raises the chance of adverse reactions like panic, dissociation, or destabilization. Do not stop or change pregabalin without the prescriber.
If considered, insist on a thorough screening: full medication review, trauma history, suicidality, any psychosis or mania, traumatic brain injury, sleep, and substance use. Use a supervised setting with experienced facilitators, clear consent, medical backup, and planned integration support.
For additional context on this exact question, see this related Q&A, and seek guidance from a clinician who knows your friend’s history.
Wishing your friend safety and support.