Who is responsible for tracking repayment when the amount was never given?

When I went away on vacation my sister paid for some excursions.

I asked her to tell me the price and I'd pay her back. She said "I can't be bothered right now, I'll tell you later"

We had this vacation 1 year and she still hasn't told me te price.

Then she asked me the other day when am I going to pay her back.

I told her when you tell me the cost.

Then she said "that was a year ago, how am I supposed to find the receipts, you're supposed to keep an eye on what you owe me."

Then we got in an argument.

Who is in the wrong here?

She told me she would sort it out. How am I supposed to know what I owe her when she didn't tell me

Who is responsible for tracking repayment when the amount was never given?
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