What should I feed an underweight 1 year old with asthma?

My doctor just diagnosed by 13 month old as being underweight and asthmatic. He wants me to increase the amount of milk she drinks during the day (normally 20 ounces). I am concerned because when I was a child with asthma I was limited in the amount of dairy products I could drink/eat. What should I feed my daughter to increase weight gain, but not interfere with the asthma? She is already very congested!!