No. No mixing. It's important to give her the proper dosage. The way I do it is to dump the powder out of the capsule onto a plate. Divide the powder into two little piles as equally as you can. Don't fret too much about it, though. A short dose today will be compensated with the larger pile tomorrow.
I use a little cube of bread dipped in olive oil to sop up the powder. Give this immediately to the hen. If she doesn't scoop it right up, pry open her beak and push it in. This is bitter tasting, so sprinkle a little sugar on the bread after you sop up the powder.