Mom has asthma, doctor gave 15 mg corticosteroids tablets daily. She has flares everyday. No sure what is causing asthma. Started 2 y back. Big help?

Oral steroids. Asthma flares are sometimes treated with oral steroids however daily steroids are typically not used and would be a last resort for asthma treatment. See an allergy, asthma & immunology specialist for further evaluation if needed.
Needs a specialist. This qualifies as severe persistent asthma, she needs a full evaluation by a specialist.
See a specialist. Asthma that causes a lot of symptoms needs not only inhaled albuterol for rescue treatments but also daily inhaled controller medicines. Oral steroids have more side effects, so they are to be avoided except for short few-day "bursts". It sounds like she needs to see an asthma specialist to see how bad her asthma really is, to make her treatment the best, with fewest side effects.