...And don't sneeze, breathe too hard or drop the pollen container, lol.
If you must pollinate where she sits, make sure the fan has been off for a few minutes and use slow even movements...as pollen can stay airborn for a loooooong time, which increases chance of your main cola's getting pollinated and stunting the growth of your bud. (the bud focuses on forming the seeds instead of forming more smokable stuff)

About dual-pollinating the lower branches:
If it's an emergency, and you are about to lose a great strain unless you dual-pollinate, give it a try, but, your seeds true genetics will always be in question. I would not pollinate more than one type of pollen per female.
Virtually eliminates the possibility of a screw-up.
Always better safe than sorry.