Thanks for visiting HCM.
causes retrobulbar neuritis
due to which there is blurring of vision. Your doctor is very right in stopping this medication. Early vision changes are reversible but may land up in blindness
if not discontinued promptly. But this kind of effect usually doesn't happen at recommended doses for 2-3 months.
Now if your sister has taken the drug for 2 months, then it can be discontinued and further treatment can be continued with rifampicin
and isoniazide. If she has taken for less than 2 months then she may need modified regimen without ethambutol for prolonged period.
Ask your doctor accordingly.