when my stroke was diagnosed, there were also what my neuro called spots of 'white matter' on the scans, which meant nothing -- just something one accumulates as one ages ... since your friend's mri was only to ensure that she had NOT had an aneurism, and there were apparently no other symptoms, i'd get a second opinion ...
just a suggestion, but i know what waiting for a DX is like, and if your friend had no other symptoms ... and on rereading your post -- i say a second opinion is definitely warranted ...