What Causes Thrombosis In Minor Veins Of Brain?

Question: Dear Sir/madam,

This is with reference to medical consultation for my mother. She has blood pressure, diabetes, cholestrol since 5 years. Although the same is always in border range (normal range) since years.
Suddenly on Monday, she had whirling/spinning movement, couldn't walk because of imbalance.
Her voice tonality weakened and right side of face was paining.

She was suddenly treated by M.D. Doctor of Monday afternoon, initially thought that she had vertigo.
Then the problem worsened and MRI of brain was done at night.
The report is normal, but there is thrombosis in few minor veins of brain (small brain) specially those that send signals to legs.
Doctor says that there was a clot of in these veins but luckily it got proper by itself, so MRI report is normal.
MRI of spine was done, NVC of hands and legs was done , potassium level was checked.
These above 3 reports done in consultation with neurophysician are NORMAL.
So M.D. Doctor which we have consulted and where my mother is admitted is giving medicines accordingly, so that no future clot is there, nor other veins are affected.
Physciotherapy has been started from yesterday and my mother is now recovering fastly. She can walk very good , hardly imbalance is there, only 10% she shakes.
Neuropysciotherapist that comes says that she has ATTREXIA, but very soon she will recover.

Request you to suggest your opinion, Still I did not understand the cause of this problem that happended suddenly.
Waiting for your reply,
Sincerely,
XXXX