C.P.
This is a good time to start teaching that there is a time and place for everything...and that we don't always get what we want.
Contradictions are part of life. Sometimes it's okay to jump and sometimes it's not. Sometimes you get a cookie, and sometimes you don't.
It's okay to say no. And it's just okay to occasionally say yes.
Work with hubby. Would it be okay to tell DD that it's okay to jump only when you or daddy say so and are there to supervise? And maybe cookies or cake might be a treat on Sundays? Find a way to compromise...a little fun and a cookie won't undermine your parenting, momma.
ETA: IMHO, it's NEVER to early to start teaching your child that they don't always get to do/have what they want. If it's a habit for them to accept what you say from an early age, it's easier to explain it further if needed when they are bigger.