I'm not Uny but I know what Uny would/has told others with kitties that have kidney problems.
You can give her the Kidney Tincture, you can find it here: Kidney Tincture 2oz
If you don't have one of those little plastic plungers the vets use I'm sure they would be happy to give you one. You would give her 1 drop per pound 3 times a day. This should really help her.
I'm not so sure about putting the hydrogen peroxide in her water because I'm sure it makes it taste like bleach which would probably cause her not to drink it so she wouldn't be getting the water she needs to stay hydrated.
I know exactly how you feel about her because I have a kitty that brings such joy to my life I can't even imagine losing him.