I don't see an issue with this if her daughter offered. But that is really generous of you to offer to send her the $300. Please note, though, that we don't allow monetary transactions on the disboards.
I know a family that was going to stay at at offsite hotel, and their 11-year old daughter offered to pay the difference to upgrade to a Disney hotel. They did that and the daughter was very proud to have contributed (and Disney gave them another upgrade when they heard the story). It was really nice.
Another instance - On the first or second DIS Unplugged podcast cruise we found out that a 14-year old boy earned enough money baby-sitting that he paid for an entire cruise and treated his mom for Mother's Day. He was so proud and happy that he did that. He was in the college program last year at WDW, and I got to visit with him.
I say kudos to these parents that allow their children to make these responsible decisions. It's not something that my own kids did, but I've seen the positive effects of the kids that did do this. To each his own.
Back to the discussion.