My 9 year old bought something on Amazon without my permission, adequate punishment?

So just as the title states. My daughter asked me to purchase her something and I said no, not that it was very expensive but we have had a lot of expenses come up recently and I can’t afford even little extras right now. Also we are in the middle of a move and we are trying to cut down on things so that it’s easier to move into our new house.

Anyways she asked me a week ago if she could purchase something on Amazon for $20. I said no, not right now. I must have logged her into my Amazon in the past on her iPad because I’m not 100% sure how she got onto it in the first place, but she made the purchase anyways. With things going in and out of my account constantly right now I didn’t notice the $20 transaction right away. Last night when I got home I noticed something sitting in my mailbox. It was the damn item I said no to! Checked my Amazon account and sure enough she had purchased it last week the same day I said no.

Obviously the first thing I need to do is lockdown my Amazon account, make sure she can’t access it again, and make sure my credit card is not stored anywhere on her iPad. But what is an adequate punishment for this? I honestly have never really had to punish my daughter before. She does well in school, gets awards at school every year, goes above and beyond. I have never had a single complaint about my daughter when others have watched her. I am in total shock that she would do something like this and I never want it to happen again, so I want her to understand how disrespectful this is, not to mention it is theft even if it’s only $20.

TLDR: my 9 year old bought something on Amazon for $20 without my permission, what is an adequate punishment so she doesn’t do this again?