I have asthma and allergies, so I see an allergist who also treats asthma (saves another trip to a diff. doctor) and I see one that I REALLY LOVE (if you want their info, PM me and I'll give it to you).
As someone mentioned below, they will test her for asthma by having her blow into a tube as hard as she can and it will register how much oxygen she's getting in and putting out and they will listen to her lungs too (they'll also talk to you to find out what triggers her difficulty breathing).
As for allergy testing, they can do it a few different ways...the way the place I go to is they have a pad of needles (that are, as mentined previously, small like the TB needles) that have the allergens already injected into them setup and they hold it to your back for a few seconds (that way it's one prick instead of 25-30) and they have you sit for 20 minutes to see if you react. They can also do further under the skin testing (I can't remember if that is if you do or don't react). I have also heard that they can just draw blood and test allergens to that (however, that takes more time and you'd have to wait for the results whereas the scratch test {I mentioned above} you get the results that day).
As for doing things around the home...it really depends on what she is allergic to...if it's dust, you'll need to dust and vaccuum more often and wash bedding more often and most likely put covers on her pillows and bed, if it's mold, you'll have to make sure none accumulates in areas that she is in (bathrooms, basements, school, etc.), if it's airborne you can get a better air filter for your furnace (that is what blows everything around the house in the winter) and get the vents cleaned, if it's pets and you have some, don't fret - she can try taking medications or I bathe my dog in an allergen reducing shampoo which makes him shed less dander (which is what people are allergic to, not the hair)...I do allergy injections and take 1 zyrtec a day and it's helped tremendously! I do reccommend the pillow covers and furnace filter, though, because we do those and they have helped a lot too (especially if you have pets)...
I hope this helps...