My DS2, who will be turning 3 next month, has asthma. He was sick a lot as a baby, very prone to chest infections and breathing problems. He was too young then to diagnose with asthma; generally doctors say they can't be properly diagnosed before the age of 2. My DH also has asthma, and that definitely increases their chances of having it.
What happened for my boy was, he was referred to a paediatrician to manage his issues, she did a lot of testing and found that he has allergies (they can blood test for that). His allergies are quite severe, it's dust mite and pollens and that sort of thing (inhalants). He was about 10 months old at that time. She put him on prescription medication to manage that, which he needs every day, and also ventolin, for times when he wasn't breathing well. By the time he was 18 months old, he was requiring ventolin at least 4 times a day, every day, and his paed made a diagnosis of asthma, and put him on a preventer. He's improved a lot with the preventer; it took a while to get the dose right, he's on an adult dose now (it's not uncommon for kids to need a stronger preventer) but he's finally under control and not needing the ventolin every day. He has the preventer every day, morning and night. We have an asthma management plan and he's still under a specialist.
It's not a nice thing to have to deal with, they can get so sick with it and just seeing them unable to breathe is horrible. The important thing is getting a plan sorted out, and getting all the information from your doctor, so that you know exactly what to do in any situation. I was always so nervous in the early days because I wasn't sure what to do, I mean I knew when he needed ventolin but I didn't know when it was bad enough that he should see a doctor, or go to hospital; I just wasn't confident in dealing with it. Now I feel more confident.
Good luck with it, I hope she doesn't have it, but if she does then it's good that you're getting it checked out now.