@mchler73
It’s all so frustrating. So sorry that you’re dealing with this!
One thing you might ask about is the differential diagnosis. If the consideration is that it might be scar, or it could be ADH, or it could be the rare cancer (missed in previous scans), or it could be DCIS - there are different features they consider to eliminate options. It might help to know what they’re basing their decision on, so you feel assured that they really are identifying what it is.

Have them talk through the features of what the MRI is showing differentiating it from what it is/not:
1) Your rare cancer had these features that would be visible in an MRI. What we’re seeing now is ___
Is it same or different, how?
2) DCIS, or ADH, has what features visible during an MRI? What we’re see now is ___
It is same or different, how?
3) A palpable, but not visible, non cancerous lump is expected to have these features seen on a MRI.
Your MRI shows ___
4) Scar tissue appears with what features on a MRI? If your MRI shows scar, how is this tissue different from any of the above? Is this scar just from manipulation of non cancerous breast tissue?
Or, it is scar where cancer tissue was removed? then how are they planning to monitor this as leftover cells could be present. A lump indicates cells are reproducing, they could be non cancerous, but may be an opportunity for any leftover cell.