I don't think you're wrong for sharing your feelings. If it keeps happening, that'd be a worry. I actually had a similar experience recently. My sister said she had bought me something for my birthday in September, but it came broken, and she wouldn't tell me what it was. She said a few weeks after that we should go to a shop and she would buy me something. I said that would be nice, but she made excuses about why she couldn't a couple of times, and I didn't bring it up again.
She admits she is a jealous person. Gift giving is very important to her, and I know my gifts have disappointed her in the past. She was also jealous of a gift I got for my birthday.
I'm not going to bring it up, because getting gifts is less important to me. She made me pancakes for breakfast, and that was perfect. She puts too much pressure on herself.
It would maybe be easier for your sister to hear if it's less about what's right and wrong, and more about why you wouldn't like it to happen again ie. "In future...", then it's less like a telling off.
How did she take it?
Why did your friend think it was wrong?