Hmmm...let's first thank the Lord above that she made it home safe. When these storms occur...all to frequently we get news of motorist that get swept away trying to drive thru "deep puddles".
PLEASE reiterate to her to NEVER drive thru water that you can't tell the depth...or if it is flowing across the road etc.
As you can see in the video below...t h e X5 can normally drive thru water about a foot high with no problems...so if this was truly just a "puddle"...the engine shouldn't have cut off. Since it did...I would venture that it was more than a deep puddle.