The problem is called "retrograde amnesia", and it is more common than you think. She needs to go to a stroke center, as of yesterday and get an MRI as of yesterday. There are many problems that can be easily resolved if caught within the "window of opportunity". She has had a yellow approach signal to an open drawbridge. And the river is very deep. If she has a stroke she can end up a virtual vegetable for the remainder of her days on this planet. Please urge her to seek emergency care.
There are a number of reasons for passing out, and typically they do not remember the events passing out. But it is strange she does not remember coming home with the walk! My husband passes out, he has had spinal headache for long time, due to an epidural injection, spinal fluid leaked.........anyway, he gets real warm in the face, and then bam he is out. He woke up on the shower floor, not knowing what he hit, just that two toes were broke, and skinned up knees real bad.. it is scary! And HE IS going to docs, and has for almost 2 years with NO real answers, and the docs keep cashing the checks, so that is even more aggravating......trying to get treatment and treating him like he has a cold! But if you look up synoscope, or vaso vagel, it should give you some info, and maybe print the interesting ones out, that may apply to her situation, and let her look at them. THere is a heart condition./blood pressure problem that can cause this, they do a tilt table test to find it, but can sometimes be detected by checking BP sitting down, then standing up. Good luck, and hope she takes this condition seriously!