Check Engine Light... Now Dead (UPDATED 1/22)

[X5_2_OBX]

The 'Check Engine' light came on in my mother's E70 last week. She booked an appointment a few days out to get it checked. She went to take it in that morning and the light was off. The service manager said not to bother leaving it which was frustrating because they are usually very good about taking it and looking it over anyway.

Fast forward to today- she's sitting at a red light and the car dies. She tries to restart the engine... makes a gawdawful sound but won't start. The headlights are on and not at all dimmed and there were no other signs of a battery problem. I can't describe the sound it was making but it was nasty sounding. Since it was darn near stopped in the middle of the intersection BMW Assist rushed the tow truck which showed up in about 30mins. In the meantime, my brother remembered that the service department was still open but only for 15 more minutes. We booked it over there and they gave us a 325i loaner... otherwise we'd be screwed!

Anyways, I tried to look up to see if anyone else has had this problem and it sounds like another member may have experienced something similar but I couldn't find any follow-up on it. Any thoughts?