When we, as human beings, have preexisting injuries it is “less-than-wise” to simply ramble into any thing labeled “yoga” AND expect a therapeutic offering. This is true of instructed group classes, privates with poorly or inadequately trained teachers, as well as books/dvd/internet streams.
While much of asana (the poses or postures erroneously referred to as “yoga”) feels “good” and may be “good for you” and brings a modicum of wellness (depending on what exactly is offered and how it is embraced), these things are not yoga therapy. Yoga therapy is not delivering a sequence of poses to people for them to feel better. Yoga therapy is assessing the student then crafting a very particular, specific, targeted protocol for what is being addressed.
Students of Yoga who have “low back pain” (an incredibly general term) should be assessed to determine what is the causation of the pain, where that causation lies, and how best to attend to it. To tell a student “do Bhujangasana for low back pain, it is good for it” is gross negligence, not to mention a dull shard of "truth.
Until the student learns how to lift the pit of the abdomen and sides of the waist, rotate the thighs and contract the buttocks, then move the sacrum toward the Achilies tendons, “cobra” is not good for the lumbar spine (read: low back). It is actually counter productive and ill-advised.
Students who remain aggressive, violent, or performing will always sustain injury no matter how sound the teachings or teacher is but that shouldn’t stop one from seeking the most sound instruction/instructor possible.
It is unlikely you will lose everything. If you gain a deep understanding of the approach to asana then you are far and away ahead of about 4/5 of all asana practitioners, regardless of their suppleness, gymnastics, or mobility. Having a rooted approach trumps open hamstrings every day of the week. Your lesson is far more profound than physiology.
I would invite you to consider attending some workshops outside of your area. If you are locked in to video education then perhaps search for something targeting lower back issues. Stay away from frisky, fast, heated practices as their level of demand does not facilitate the mindfulness required in doing safely, especially in lieu of injury.
Warmly,
gordon