Unless you want to further injure your lumbar spine, I would avoid flexion at that level. You should strive to keep a brace, locked, neutral spine from the C-Spine all the way down to the T-Spine. BUT, during competition weight lifts, some thoracic flexion is expected.
This does not mean it makes the lift easier, it is more just a minor slippage in form due to the extreme load being moved. During competition level lifts, that small slippage of form is generally acceptable (most people are not powerlifting for the sport of powerlifting, so they should focus on maintaining proper form/technique).
I may be putting words into your therapist's mouth, BUT you may be over-extending at the lumbar spine, rather than bracing at the lumbar spine and extending at the hips, during your lifting technique. Why not just post a video of your technique on here?
Also, which direction were your disc injuries (anterior, posterior, etc)? Also, did you have "ruptures" or "bulges"? They are two very different injuries.