I think you'll be fine. I WOH and basically stopped pumping at work 12hr shifts 3 days/week ) just after a year and didn't have any issues. Awesome that you want to help your sister. You could always get a hand pump (if you don't already have one) to use on this rare occasion that you need one.
[SIZE="3"]Married to Mike~ Proud mama to Mackenzie (13),
Madelynn (9) ,Marleigh (25months), and Noah (11months) We are a