Any advice on how to help my baby with allergies

My little one has Asthma and we have tried everything from getting allergy proof bedding , re-housing our pets , vacuuming our house everyday but looks like she shows no sign of improving . We recently started her on immunotherapy but its making her very weak. I feel helpless. A close friend of mine mentioned that most of the HEPA filters are good to get rid of pet dander and dust but when it comes to viruses which cause influenza it doesn't really work. She also told me they release ozone which can further irritate the lungs of my baby. I'm having second thoughts about these air purifiers...Not sure I need to buy one now. Can you advise me please!

I can't help with the therapy, but I did fix my dust and dander without ozone.

I had the furnace man put a box for the larger 4" filters on my air return. I also have a motor with 2 speeds, so it can run on low speed 24/7. It only costs about as much as a 100 watt light bulb to run it.

My housekeeper is very happy not to have to dust much at all, and I have a cat, whole house carpeting, lots of stuff that makes dirt and mites.