Thank you all for your perspectives and advice! I'll ponder the idea of a low limit credit card that's still linked to our account, and I'll go read about the 'prepaid' credit card option. If she loses the card, for example, would the money still be available to her with a replacement card?
She is responsible, but she's also 14. I want her to learn and not get frustrated.
I have an Amazon Visa card that I'm not using. It has waaaaaaaay too much credit, so that would have to change, but I wonder if I could get her name added to the account and get a card in her name. The bill would be all hers, since I'm not using the card, and I could show her how to transfer money from her savings account to our checking account each month to cover the charges.
We started her off by with loading $15 on the Starbucks app on her phone. I know, I know, but just hear me out. Her dad loaded another $15 this past weekend, and she said she didn't know where the previous $15 had gone, so she went back through her purchases, and sure enough, they added up to $15. While Starbucks is of course spendypants galore, it taught her the "little things add up" lesson in ways hours of lectures from me never would have. Money well spent, I say.