My oldest son uses Pulmicort as needed, though he doesn't have asthma. (He has another condition called 'Cronic Croup', and the Pulmicort really helps with that.) He has taken it for a couple of years now, and we've never had a single problem with it. As a matter of fact, I consider it a miracle drug...before the Pulmicort, he had to take all kinds of other stuff that sometimes worked and sometimes didn't, and the stuff was oral and tasted like drinking fire (I tried just a tiny taste and it was horrible!). He would scream and cry over having to take it, which only made things worse. The Pulmicort is given through the nebulizer and really doesn't have a taste...certainly not a bad one. Bry doesn't mind taking it at all.
One thing to remember with the Pulmacort is that it's a maintenance medication...it will not stop an asthma attack, it just helps to prevent them from happening. (On a twisted side note, it DOES stop a sudden Cronic Croup attack...funny, huh?) If your daughter ever gets really wheezy, short of breath, or complains of her chest hurting, then you will need to call your doctor right away...they may want you to bring her in so they can give her a different medication to stop those symptoms. I would even ask them if there's not something that you can keep on hand just in case she ever does have a big asthma attack. I don't know what's available for little kids, but they'll know.
I don't know much about childhood asthma, either, except that my best friend has had it since she was a child (diagnosed at age 7) and apparently you don't outgrow it. But she has learned to adapt to it...she instinctively knows what her limitations are by now and avoids (when possible) her triggers. For instance, a big big trigger for her is chlorine bleach, so she doesn't use it when doing laundry. She uses a non-chlorine bleach when needed, and everyone else avoids using it on their clothes if she's over for a visit.
As for adult-onset asthma, yes, it's extremely possible. I was just diagnosed with it a week or so ago myself. And I'm 31, getting ready to turn 32 next month. The breathing test the doctor had you do was a peak flow test, it sounds like. The idea is to test how much air you can move before a breathing treatment, then to do a treatment w/Albuterol, and then see how much air you can move afterwards. They did this with me several times over the course of 3 hours, and thanks to the Albuterol and a couple of other drugs, I went from a peak flow of like 80-100 up to a peak flow of around 400. There are normal peramiters for each age/height category, and as long as you fall fairly close to the right one for your age/height, they don't worry too badly. Now that I have been diagnosed, they gave me a peak flow meter and a chart for me to use to keep track of my rates here at home. Personally, in making the diagnosis with me, they asked questions, took a blood test, and did a chest x-ray. It didn't hurt that I arrived there in a full-blown asthma attack, either. They seemed to know what it was right from the beginning, but did the other stuff just to confirm their diagnosis.
I hope this has helped some! Like I said, I was just diagnosed with it, and this is mostly stuff that I've picked up from talking to my friend, my doctor, searching the internet, and my own (or my son's) experiences.