I highly recommend reading "Taboo or To Do? Is Christianity complementary with yoga, martial arts, Hallowe'en, mindfulness and other alternative practices?" By Ross Clifford.
https://www.amazon.co.uk/dp/0232532532
This takes a non knee jerk, non ignorant approach to the subject, as opposed to websites such as Got Questions which are more fundamentalist driven. You'll find properly reasoned conversation about what is and isn't a good idea within yoga, which generally boils down to exploring what is happening spiritually. It definitely should be something you check out as a yoga teacher and might surprise and encourage you, helping shape your practise so it stays holy and helpful to people.
Crystals - look lovely (I have loads as a degree qualified minerals engineer), and certainly quartz has piezoelectric effects, but I'm struggling to see how much else in Crystal therapy has any basis in reality, other than placebo effect.
Meditation - the influencer probably comes from a fundamentalist sect which doesn't really value loving God with all your mind. They also are shallow thinkers as a result, preferring easy answers that are binary black and white. Meditation in Scripture is abundant, and clearing your mind to focus upon God has been the mainstay of two thousand years of tried and tested Christian meditation techniques such as Lectio Divina, labyrinth, silence, the Cloud of Unknowing etc. Ignore the fear inducement from the influencer and don't let them tell you it opens your mind up to negative demons infiltrating you - that's the quasi theology of Frank Peretti and co... if we opened ourselves up unintentionally through altered of consciousness, we'd be susceptible to demonic influence when sleeping, daydreaming, etc... you have to deliberately invite demonic influence in to become infected internally. Shallow thinking is the order of the day for modern evangelicalism I'm afraid.
To Do or Taboo by Clifford and Johnson is a well researched, down to earth guide to help Christians think for themselves whether or not something is a go or a no...