How do I prevent asthma attack of my wife, likely to happen every year in march/april & oct/nov? Is there preventive (non steroid) medicine?

See a doctor. She should see an allergist or pulmonary specialist who can help her with this.
Sound like allergies. These appear to be the two likely seasons for pollen or ragweed allergies. If this is the case talk to your physician about using an antihistamine during these months. This may reduce the number and severity of her attacks. You may also want to consider having her tested for allergies (skin tests) just to make sure.