Thanks for your input Curious, you make a very good point that the punishment should relate to the infraction. How would you punish things like disobeying an order while training or acting without permission?
I suppose that would be very dependant on what order was disobeyed or what was done without permission. It is a bit hard to relate it to the infraction in broad hypotheticals, thus the need for you to be creative when it's time to punish.
Asking for ideas for tasks is understandable, especially if you're new. It's a bit hard to just throw things out in the open without having any clue of either of your likes, dislikes or limits are. I'd really suggest doing some research. Between kink talk and get dare I'm fairly certain there are no less than 634,821 ideas floating around to spark your interest.
What I find concerning is your sub has yet to fail and you're anticipating punishing her. This is a bit frightening because as a Dom, I don't think you should really want to have to punish her. Punishment is for disobedience, infractions, not following the rules, this isn't something you should find appealing. If the idea of pain or spanking turns you on, find a way to incorporate it into play but you should never want to find a reason to punish her. The psychological impacts of punishment on someone who's desire is to please is difficult. If she sees this, you have also instilled you have no confidence in her ability to please you. Not a great thing for a lot of reasons.
D/s needs to have a lot of things considered, especially when considering punishment. It requires understanding individual capabilities and needs. It's more than just about having someone to boss about and cater to a dominant's whim. If you have doubts she'll meet your expectations, you need to either reexamine your expectations or you should have never take her in as your submissive to begin with.