Oh Hun, I have to agree with everyone else, that you might be doing more harm than good. I think you should stop expressing the anal glads, I think you should stop trimming her hair around her pee area. She probably has very sensitive skin and it must be irratated.
I am not sure what food you are feeding now, but if it has Corn (corn in any type of text) and By-Products (in any form of text) I would STOP it immediatly.
Raw food diet is what I feed my 2. Either
www.naturesvariety.com or
www.morigins.com
If you must feed a Dry or Wet, try
www.naturalbalance.com - they have a Duck and Potato flavor, which I do believe is very good for allergies and sensitive issues. Also,
www.canidae.com is a very good dogo food.
I also feed my 2 - Dried Cranberries and Dried Blueberries everyday. They get about 3-4 of each. I buy them at Trader Joes or Costco (Human Food).
I also feed 1/2 teaspoon of Organic Low Fat Stonyfield Yogurt and I sprinkle some extra Probiotics that I bought from the fridge section in The Vitamin Shoppe.
I also feed 1/2 teaspoon of Orgainc Extra Virgin Coconut Oil.
All the things I have mentioned, you can do a google search and find lots of stuff relating to overall health benefits.
Relating to your girl, my female in the past would have 'scooting' if I too trimmed her hairs too short, or if the buzzer was too close and gave her 'razor burn'. She too gets a small build up of 'blackish', but my Vet just said it is normal, dirt like, and I just need to wash her gently more often.
Again, I think you should stop the anal glands and stop trimming her hair, just rinsh her privates under the sink with a gentle baby shampoo. Try changing her diet too, NO CORN and NO BY-PRODUCTS.
Please keep us updated and I hope she gets better soon