Maine coon allergic to dust mites. !HELP!

Cali, my youngest is allergic to dust mites, skin scraping has been done and detected it.  We live in a apt that is from 1917, i keep up with the cleaning and try to bathe atleast 1 a month i dont want to hate us so thats prob as much id do. The vet recommended a shot made by Heska labs that would be made specifically for her.  This shot is 200$ every couple of months and it may not even work. Im at my wits end with it. I try to avoid antihistamines due to she gets all loopy even with the smallest amount. I currently add fish oil to food just to try and save the hair that she still has.All night long i just hear her itch. theres only so much i can do to keep the dust levels down due to her ya know being a cute little cat and rolling all over the floors. Does anyone else have this issue with their kitty? im just so lost. i feel like i have tired everything with her. Ya think if i had her shaved that may help? I need to change vets due to mine is not much help. here are before and after pics:

BEFORE:

I don't see how shaving her would really help, as dust mites are in carpet, upholstery, etc, and are being sloughed off your skin, as well as hers  Here are some tips for getting rid of them, or keeping their numbers down, at least, from MedinineNet.com:

Preventive Strategies for Dust Mites

• Use a dehumidifier or air conditioner to maintain relative humidity at about 50% or below.
• Encase your mattress and pillows in dust-proof or allergen impermeable covers (available from specialty supply mail order companies, bedding and some department stores).
• Wash all bedding and blankets once a week in hot water (at least 130 - 140°F) to kill dust mites. Non-washable bedding can be frozen overnight to kill dust mites.
• Replace wool or feathered bedding with synthetic materials and traditional stuffed animals with washable ones.
• If possible, replace wall-to-wall carpets in bedrooms with bare floors (linoleum, tile or wood) and remove fabric curtains and upholstered furniture.
• Use a damp mop or rag to remove dust. Never use a dry cloth since this just stirs up mite allergens.
• Use a vacuum cleaner with either a double-layered microfilter bag or a HEPA filter to trap allergens that pass through a vacuum's exhaust.

There are different types of antihistamines...maybe a different one would work better for your little one?  And there are other things that MIGHT work...steroids might work, and certainly the allergy shot you referenced might be worth a shot.  It's costly, yes, but if it works, it's worth it, right?  I wonder if you got Pet Insurance if it would be covered? 

If antihistamines are making her loopy then it is not the right one. I personally give my cat Zyrtec. There are other safe ones as well. Poor baby. Why not use prednisolone in the meantime?