Asthma and Infections

Hi

My girlfriend has asthma she is 27 and was diagnosed with asthma after a chest infection, is this common?

also every so often she has trouble with her breathing and may need to take steroids to help she invariably gets chest infections aswell which seem to accompany the bad breathing. i want to know how common it is to have so many chest infections and is this down to the inhaled steroids ? she also takes singulair (i thionk thats what it is called) could this be the reason for the numerous infections. any info would be a great help,

many thanks