I want to pester my sister to use a Groupon I bought for her birthday.
That's strange. Why pester her about that?
She sometimes ridicules me over my bad spending habits.
Instead of pestering her for petty reasons, why not prove to her through your own actions you can wisely handle money. Try to use a financial mobile app to help you track and control spending.
My sister is such a jerk, why does she not just go pester mom instead?
She might care about you and worry about you, but you are right she should not pester you. It will not help you if you feel like she is nagging at you and it will not make it more likely for you to listen to her.