Just checked with Mom- 10-12 drops would be great. So right now, she pops off the cap (forgive the terminology) and puts 2-3 drops right on the atomizer.
I assume with these the drops go into the cap itself?
For the best results you should have her remove the inner liquid capsule from the carts, remove the filler (cotton like material), fill the cartridge about 3/4 full of liquid, replace the filler, then top the liquid capsule off with a couple drops of liquid. Insert the capsule back into the plastic cartridge and she should be good to go. With the extra capacity carts she will get a lot more puffs out of the cartridge (most likely 5 times or more than the dripping method).