Could anorexia have a part in an asthma attack?

Not directly. Anorexia nervosa has not been associated with causing or inciting asthma attacks, but certainly a patient suffering from both is vulnerable to the consequences of asthma. Late stage anorexia often results in arrhythmias, dilated cardiomyopathy, and etc, making death from an asthma attack more likely. Further, i doubt an anorexic would take Prednisone willingly, again worsening risk.
No. Athma attack results in lowering of oxygen level in blood. Affected individuals feel shortness of breath and hyperventilate to increase oxygen level leading to swallowing of excessive amount of air. As a consequence, young children often feel nauseated or actually vomit during the asthma attack.